Again, it's all riding style. If it's really rough, you're gonna hafta work it up there, and get a little run at it, or at least have some momentum.
The 4x4's are very heavy, and there weight helps them to climb things slower, because they have a little more traction from that weight. 4 wheel drive is a plus to anyone who likes to ease through the ruff stuff. Personally, I prefer 2wd, I just think they're more fun.
After over 20 years of extreme riding, mud, snow, mountains(haven't got to try sand dunes...yet) I've ridden just about every Japanese 4 wheeler out there. I've never not been able to go on a 2wd where a 4wd went. I would have to ride alot more agressive to make it up and through some things, but again, that's just how I like it.
A Raptor has great tourqe, speed, suspension, and comfort...with electric start and reverse. They are also very dependable. You can't go wrong for $3500 if it's in good shape. It's just all up to how you like to ride