What fuel for Polaris sportsman?

It really depends on the engine. You shouldn't use ethanol mixed gas in any of them, but really the only one that will give you troubles is the 850. The 850 is very picky about fuel, and poor fuel can make it stumble and not run at all. Run only high-octane, non-ethanol fuel in an 850. The older 500 and 800 engines will run fine on pretty much any pump gas.