I have both a Polaris 570 and a Yamaha Grizzly 550. The Polaris to me is a much smoother ride and the grizzly seems to have more power. 4wd on the Polaris is smoother shift on the move while the grizzly is much more utilitarian in execution. Love them both and if I could only have one, it would be a tough decision, but I most likely would choose the Grizz.
Steve