I think the RZR4 should win. Polaris, through all its struggles, has made something the whole family can enjoy and thats a big reason to buy these toys in the first place. I was rather impressed that even my 6' frame could get in the back seat and be compfortable. They have a sturdy and stable feel and stance to them and still feel sporty.
Plus, look at the racing plattform for us desert guys, the exrta wheel base is a plus in the whoops section. Polaris has my vote.