Not MTBs as such but I think that it bears comparison....the work/touring/club run bike that I used up to a couple of years ago has 26" wheels, it's now been largely superseded by a 700c bike which is fairly similar apart from wheel size. I take in lots of crappy, poor surfaced cycle paths and tracks, plus plenty of wiggly bits around barriers etc...so similar to MTB-lite, but made a little more interesting by the use of slick tyres.
My overall impression of the change is that the 700c rolls a lot better over the minor bumps and lumps, making it a tad faster and more comfortable. But it's much more effort to get it around the wiggly bits, I assume because of the extra length.
Thus I would say that it's a case of deciding which area your riding needs most help in. In my case, when I MTB, I don't have too much difficulty powering along on lumpy tracks, however I do find that the wiggly technical bits are more challenging, thus I would think that 26" suits me better. I've some friends who are technically very good but just not that fit - they seem to like 29ers.