I rode 26" all my mtb-ing life and will choose that size again when I hopefully get another mtb.
29er is a fad and nothing more. Thorn (I think it was them) did a test to see if there was any difference in ride quality between 26" and 700c and found very little between them. So they stuck to 26" as it's easier to find tyres in that size, anywhere, not just in Tibet.
Mountain bikes are supposed to be nimble, light, strong and have decent mud clearances. Bigger wheels require bigger frames reducing the nimbleness for certain sized cyclists. The extra material used to make bigger rims and tyres adds weight (although little). It's easier to bend and break a longer stick than a short one so in my mind, the same applies to longer spokes and clearances between frame and tyre will be smaller unless the frames get bigger, again, bad news for shorties like me.
With any luck, the idea of 29ers will go the same way as URT suspension frames
and Cannondales famous but amazingly more stupid one legged suspension fork (if there was a facepalm smiley I'd use it here).