For me, personally, they roll over smaller stuff that I'd end up eating a little smoother. It feels like they roll a little better, imho. I think the wheels feel stronger and I sit where I'm a bit more confident riding. I'm 6' with a 30" inseam.
The one thing I've found that 29ers excel at is taking average and below-average cross country riders and turning them into sanctimonious snobs.
Haha, I can relate...
NJ, I think some people like them because they've got a Clydesdale ride... big, stable, forgiving of "monster-trucking" stuff, and hard to flip. For a lot of people, maybe that's the right thing. Personally, I'm an XC racer and my top priorities are fast acceleration, high maneuverability, fast climbing, and fast flat-out cruise speed, all of which my 26" race bike does better than a high-end 29er in my size.
Anyway, if possible, try equal-caliber bikes from both camps and see what you like.
I'm far from sanctimonious, unfortunately. As I said, for my size, I'm more content on a 29" wheel mountain bike. I'm closing in on being sub200 again, and I don't foresee going back to a 26" wheelbase again. That is a "now" statement though, and could change in June when I buy my Specialized Epic.
Ride whichever feels better to you, and if the LBS near you doesn't have options for you to test, take a little trip far enough to get to one that does. You'll have a lower chance of buyer's remorse.
In an out and out race, I believe I maybe faster on a 26 inch bike. I own a Ti 29er hardtail and really like it. I like it because I can ride it hard for an hour and feel less beat up than on an equivalent 26 inch hardtail. The difference in speed isn't enough to bother me either way.
No doubt a 29er doesn't accelerate as fast as a 26 inch bike. But keep in mind there is a reason that road bikes evolved to 700c wheels.
Once spooled up the big wheels really go.
I am not a snob in that I see room for all bikes. A lot of top racers have not made the conversion to a 29er for the simple reason that a 26 inch bike can be built lighter, it handles quicker and accelerates faster...admirable traits when out on the trail. I like to blast groomed trails without a lot of turns and for that a 29er is taylor made.