The big bike companies are pushing 29ers pretty hard. My best guess: they'd like to standardize adult bikes on one dominant wheel size (700C/29er) due to economies of scale and higher profit.

I don't like them, never ridden one yet that made me wish for one in place of either of my 26" bikes (and as I work at an LBS, I get to ride a good selection of them). In my case, the biggest objections are that the bigger, heavier wheels are harder to accelerate than an equivalent 26" wheel, maneuverability suffers, and of course everything is about 10% bigger/taller/longer/heavier, including brake rotors and cassettes, for equivalent strength and functionality.

One eye-opener for me, was doing a long road/gravel ride with a guy on his high-end 29er and coasting away from him on all the descents with my high-end 26" bike. And he outweighs me by probably 80 pounds. So much for the "big wheels roll faster" tagline that's a favorite of Large Bicycle Company "T". Anyway, it corroborated what I experienced when I rode his bike myself... slow, compared to my XC 26er.

Some folks have a borderline religious fervor for their 29ers for various reasons, so in the final analysis, get whatever makes you happy.