Polaris synthetic in every one I've ever owned. Great Stuff, IMO of course I always run what the MFG recommends & change mine as sceduled in the Owners Manuel. Pretty cheap maintenance, I figure ts money well spent.
I use Mobil 1 0W40 in my Polaris. It seems to be the preferred replacement oil for Polaris engines. Polaris oil is rated as 2W40.