both are decent years, the polaris will need new pistons more often, change em out before they break. cats are kinda bigger sleds than pros, will take getting used to coming off a pro. better suspension if you pound it. upgrades for days, you can go crazy making the cat chassis better but really doesnt need stuff to be reliable. skinny tube boards would be a big upgrade, quite a bit of work, and id make sure it has newer 21/49 gear ratio if its 7 tooth drivers/3". i think thats what '17 limiteds came with check the parts diagram tho.