New tires on grizz 660 advice Farm tires/mud tires?

I al needing new tires on my grizz 660 and need some advice. I live in ND on a farm so i use it everyday but i also want tires that i can take in the mud every once in a while. I am looking at maxxis bighorns but i am not sure. I am also thinking about staying at stock size. Any advice wouls be great thanks.