for the big 4x4s, I have a rincon that is lifted and whatnot. Got it for cheap, so I can't complain. My cousin had a brute 750, and that was nice, w/ plenty of power. I think the honda was more comfy IMO, but the Brute def had a lot more power stock (I have the big 3 on mine plus some LOL). Can't say much about Yamaha, and the polaris problems have gotten better w/ the belts slipping but I'd still shy away from them. Overall, what are you going to do w/ the 4x4 is the main question. B/c there are so many factors to consider. If you are gonna be hauling a lot (trailer/whatnot) I would probably try to get one w/ a manual tranny as the CVT's aren't the best for that sort of stuff. But if you're looking to go mudding or something, any of those 3 would be fine, throw some mudlites on there and have a blast. A lot of people like the idea of power sterring offered on some of them, but honestly, I think it is just something else that will break. If you are lookin for some deep mudding and stuff, Arctic Cat has the one w/ a snorkel already built in as well that I haven't heard anything bad about yet.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!