The 135/2L and 200/2.8L are the sharpest lenses I've got, with the 200 actually a bit better than the 135. Not just the center, but all the way to the corners on a full-frame 5D. For comparison, I also have the 85/1.8 and 300/4L IS and while they're quite good, they're not up to the overall excellence at any aperture of the 135/2L and 200/2.8L. I always try to stop down at least one stop from max aperture with the 85/1.8 and 300/4L IS. I also have the 100/2.8 macro, which is a very good lens, but I use it for such different subject matter that I can't make a fair comparison.
I've never used the 70-200 zoom - just too big, heavy, WHITE, and expensive for me. For a zoom I use the 70-300DO, and I've been very pleased with it. Processed through DxO Optics software it's darn good except the extreme corners at wide-open apertures. It's relatively small, light, and unobtrusive.
I think it would have to come down to how you're going to use the lens. Primes are fantastic when you can control your position. For many landscape situations you can't position yourself precisely where you'd like, so a zoom can often get you slightly better framing than a prime. If the 70-200 is as good as it's rumored to be, better framing may be worth it. My experience has been that fewer pixels through better glass produces better prints, though. For example, if ideal framing required, say, 185mm then a 200mm prime would be too tight and you'd have to drop back to 135mm and crop later if using only prime lenses, or you could set the 70-200 zoom to 185mm and use all of the pixels your sensor has available. Which would produce the better print? It's probably splitting hairs, really - nothing that would be noticed until at least a 12x18 print, and maybe bigger.
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