Depends on what kind of riding you want to do. ATVs are like boats-- you can't do everything with just one.
For busting brush, hunting, and woods riding, my personal favorite is the Honda Foreman. I've ridden Ranchers before, good rigs, but I prefer the bigger bore and shift-on-the-fly 2x4/4x4 option on the Foreman.
If you want scary-type, pull-your-arms-out-of-your-shoulder-sockets performance out in the dunes, go with one of the big bore 2WD hi-perf rides. IMHO, Honda and Yamaha seem to be a little better than the other makes. That's just my taste, though.
I like Polaris snowmobiles above the rest, but I don't care for their ATVs.