I have a full size Ranger that I used Amsoil in for years. I found a convenient way to purchase Lucus and switched and have been pleased with it's performance as well. As far as the RZR, I'm about to service it for the first time this weekend, putting either Amsoil or Lucas in the gearboxes, and Dino oil in the engine for another 35-50 hours to be certain it has been properly broken in. Amsoil and Lucas are both considered premium oils. BTW, Polaris recommends 0-40 engine oil, but have heard of many other weights used in summer also, especially in extremely hot areas.
I have always used Amsoil in my ATV's and can buy it for a BUNCH cheaper than Polaris oil. I just made my 25 hour service with Polaris products but was thinking about changing to something more cost effective.