-- The set of primes weighs about 10.4 pounds, the zooms
weigh under 4 pounds, and I have to hike with these.
-- The primes are not sealed against dust and water, and they would often see dusty and rainy conditions.
-- Different brands render colors differently, but the wider Sigma lenses perform better and cost less than their non-apochromatic Zeiss counterparts.
-- The primes are less versatile than zooms and do not cover the long end of the 24mm to 200mm range.
-- The Zeiss primes are manual focus only. This doesn't matter much for landscapes, but it limits the use of the lenses for anything else.
While I was pondering all of this Canon announced the 5DS and 5DS-R camera bodies. If that had not happened there would have been no other choice3 and it would have been a James Glasgow Farragut moment. He's the guy who said "Damn the torpedoes, full speed ahead!".
My opinion is that Nikon will remain king of the hill in terms of pixel quality at low ISO settings for a very long time, courtesy of Sony. Sony is an electronics powerhouse that makes image sensors for everything from point and shoot cameras to the medium format Pentax 645Z. Their expertise in this field is unmatched. I'd expect the next generation of Sony image sensors to match or beat Canon's resolution and they'll definitely have better low ISO dynamic range. It's the sensor to have, but I don't want to carry 10 pounds of prime lenses and deal with all the other issues listed above in order to get some extra dynamic range. Preliminary test images indicate the Canon 5DS /5DS-R will resolve a little more detail than the Nikon D810, which isn't bad. Canon has also reduced shadow noise in 5DS and 5DS-R by about 1 stop at ISO 100 relative to its predecessors, and the remaining noise is much more random. Noise reduction is much more effective on random noise than it is on the pattern noise that has always plagued Canon image sensors. All of this will help or cure most of the issues I deal with. Being objective, I encounter issues with shadow noise when shadows are significantly "lifted" much more often than I encounter dynamic range limitations. In addition, noise in prints is reduced when files sizes are this big because less enlarging is required to make a print of a given size. I don't encounter dynamic range limitations very often and I'm able to handle some of them with multiple exposures, though I'm the first to admit it's a pain. The dynamic range limitations I can't overcome will still bite me in the backside once in a while, but that's life. For me at least, it doesn't happen often enough to warrant carrying 6.4 extra pounds of equipment or give up anything in the way of lenses for all of the other photos I take. I'll settle for the extra resolution and reduced shadow noise. Like the song says, "two out of three ain't bad", and I get to keep a bunch of lenses I'm quite happy with in addition to avoiding the hassle and expense of selling lots of equipment. It's a bonus that I could use a 5DS-R on the long telephotos for landscapes occasionally, and in a pinch I could use it as a backup to the 1DX if something bad happened to it while I was away somewhere. I am disappointed that Canon has not been able to increase dynamic range a bit more in the 5DS and 5DS-R, but I'm very certain this is the best system choice for me. With all of that said, it is important to keep in mind that this camera is optimized for use at low ISO settings and it tops out at ISO 1600. Mine will be used at ISO 100 nearly all of the time and it is unlikely to ever see use above ISO 400.
No camera will make anyone a better photographer, and no one will gain or
lose a customer because they used a particular brand. When used properly all
of today's cameras and lenses are "good enough". Things like photographic
technique, subject matter, composition, uniqueness, and color are far bigger
factors than equipment in the success or failure of an image. In fact,
equipment choice is probably the least important factor. But we all want the
"best" when we're purchasing. The problem is that no single company has the
best image sensor, widest selection of best quality lenses, best camera feature
set, and best everything else. That forces us to choose particular qualities
and sacrifice others in the process. There is no "best" system, only systems
that are better in one way and worse in another. I'd be in heaven if Nikon
would make a version of the D810 with a Canon lens mount. They could call it
the D810-C, and I'd buy one in a heartbeat. In fact I bet many would. Until then life is indeed a compromise on both sides of the Canikon
Happy pixel peeping.
P.S.: Another system consideration was service and support. The more equipment you have and the more you use it, the more necessary it is to consider this. For service turnaround time and out of warranty repair cost, Canon wins by a mile. If you belong to Canon Professional Services (CPS) the turnaround time is between 2 and 7 business days depending on your membership level. Without a CPS membership "professional" camera models still get expedited treatment that usually takes 10 business days or less. I've personally seen non-CPS repairs that were turned around in 3 days, but I can't attest to how normal that is. CPS members also get free maintenance service for a certain number of EF lenses and camera bodies per year. Again, the number depends on the level of membership, but it's quite a good deal. By contrast Nikon service turnaround is measured in months and out of warranty repairs are much more expensive. Please see the "Service and Support" section of this article for some other facts about Nikon service from a very knowledgeable person with hundreds of first hand experiences.
1 I mentioned that if I completely switched to Nikon I would need a Nikon D4S for birds and wildlife. Basically, a D810 is not the right camera for this task, though it can certainly be used. Camera bodies with lower voltage battery packs, like those in the Nikon's D810 and Canon's 5D series, are not capable of moving the elements of super-telephoto lenses as fast as cameras with higher voltage batteries like Nikon's D4S and Canon's 1DX. That means they cannot lock focus as fast with those lenses. Battery grips add capacity but do not provide the higher voltage (about 11 volts vs. 7 volts) necessary to affect focusing speed. In addition, above ISO 800 the D4S and 1DX perform better than the D810, and such ISO settings are very common in bird and wildlife photography. For example, both the 1DX and D4S both have more dynamic range than the D810 at ISO 800 and above. Finally, one can certainly photograph birds at 5 frames per second, and I did that for years, but from experience and comparison I know many good shots are missed between frames at those speeds. For instance, getting the wing position you want takes some luck and is very sporadic at 5 FPS but it's nearly guaranteed at 12 FPS. A D810 can shoot 7FPS in DX mode, and that can be a help if one also wants a "crop factor" along with it. I'd personally rather crop later during processing, if at all. The crop factor can help if your lens isn't long enough, or hurt if you end up with too much lens for what you are photographing. The bottom line is that if you can't get the picture in the first place the image quality doesn't matter.
2 When comparing lenses there is a lot to consider beyond resolution. To start with, there are "The Seven Deadly Aberrations" that include longitudinal chromatic aberration, lateral chromatic aberration, spherical aberration, coma, field curvature, astigmatism, and distortion. For instance, it's quite common for a lens to develop field curvature at real world "landscape distances". This is what keeps Tamron's 24-70mm f/2.8 from beating the Nikon version. It's also somewhat common for wide aperture lenses to have a slight shift in the plane of focus when stopped down. If it's significant there is no good way to deal with it. In one Nikon prime lens I looked at, the depth of field added by stopping down was always away from the camera, and the front of the "sharp zone" never moved from where it is at the widest aperture. What's actually happening is that the sharp zone gets wider in both directions when stopped down, but the plane of sharpest focus also moves backward, keeping the front of the "sharp zone" stationary. Software can't help with most of these aberrations while others are correctable, and some corrections extract slight cost in image quality. In addition, things like water and dust sealing can be very important if you need them.3 There actually are other choices beyond Canon and Nikon, such as Sony. I briefly looked into Sony and other cameras but ruled all of them out for the same reason. None of these other brands offer the lens range of Nikon or Canon, from super wide to super telephoto to tilt-shift, to macro. Instead of picking the right lenses for what you do, you must fit what you do to the lenses that are available. There are third party adapters that would allow the use of my existing Canon lenses on a Sony camera, but I found there is wide sample to sample variability in these, quality is spotty, autofocus is too slow for anything but stationary subjects, and various firmware glitches exist that have crazy workarounds like dismounting and remounting the adapter or turning the camera off and on to reset it. The last thing I want is some squirrely adapter system that doesn't work when I need it to without a song and dance. Too many opportunities are lost while you are busy coaxing things to work. In addition, some Sony cameras (A7, A7r) use a lossy compression algorithm on their RAW files.
One last personal rant directed at Canon: It bugs the heck out of me that Canon 5 series cameras have no built-in eyepiece shutter. There's just no excuse for that. Fumbling around with a cheap plastic eyepiece cover that will eventually get lost while you're trying to quickly take a photograph in the wind and rain is absolutely ridiculous! Flipping an eyepiece shutter lever becomes automatic and takes perhaps a quarter second. Without the eyepiece shutter I'd use only manual exposure rather than fuss with make-shift light blocking methods that fall off or flap in the wind and help to create blurry photographs. It sounds minor, but it affects exposure which is incredibly important, especially when there is limited dynamic range! People say it's better to use Live View, which is fine when there's enough time on a nice day. When standing in pouring rain, waterfall mist, or blowing sand it is far from optimal. When you need to compose and shoot quickly there's nothing like a DSLR viewfinder. That's why they exist! When you do that on a tripod and need to take your eye away momentarily without letting in any light, an eyepiece shutter is more than a nicety. The Nikon D810 has an eyepiece shutter, as do Canon's 1D series cameras, but for some reason Canon couldn't incorporate one in the $3900 5DS-R, which is obviously meant to be used on a tripod. What were they thinking?
Some helpful camera and lens rating and review sites:
https://www.lensrentals.com (See articles and blog)
http://www.dxomark.com/ (This is useful only for comparing different lenses on the same camera because lens resolution scores are based on the specific camera/lens combination. In other words, the world's best lens on a low resolution camera will have a low score.)