I'd love to do the Divide. Maybe in a couple of years. Anyways, I talked with a guy who recently did the divide on a 29er. He said he'd use the 29er if he were to do it again.
He did mention some nasty sections of washboard and some perilous sections where water was scarce. Sounds like a blast.
If I were to do it I'd probably use a 26" hard tail and a BOB trailer mainly because I don't want to add another bike to my fleet.