My first mtn. bike was a freakishly heavy and sluggish 26er...new ride is a faster/lighter 29er. It's hard to compare the two, since the 26 was such a dog on uphills and I struggled to keep up with anyone. I really like my 29er (well, I did before busting my wrist in Nov. I've not been on it a whole lot on trails since then, since my focus now is continuing to heal my wrist and train for an olympic distance duathlon in July), but I wish I'd had some 650/27.5 bikes to try, too. I'm just under 5'4", so something splitting the difference between 26 and 29 would likely have been ideal. The shop we'd frequented when I was shopping didn't carry any 650 models. The shop we are now frequenting (after a bunch of ugly politics had a lot of people jumping ship) does carry some 650/27.5 models. Bad timing.