Some swear by NGK, some by Champion. Champion has a part number made specifically for Polaris, NGK doesnt. The NGK is not the exact same equivalent as the Champion. But some people still swear NGK run better in thier Polaris. Run whatever you feel like. I personally use champions, never ever have fouled a Champion in anything. I have fouled plenty of NGK in my old Quadracer days. Then I switched to Champions and never fouled another, and they were cheaper. I have 8000 miles on my 08 Poo and have changed plugs 3 times, once for blown motor, once for bad stator, and once because my spares were new and had been just sitting there for 2 years.
Try both, and decide for yourself. See if you can tell a difference.