There is no best hat. Buy whichever has stats that suit you best. My sb has low def and res, and i value luck more than skill. So i have wolf hat. If you want to block more hits, get cheetah hat. If your char is shaman, probably bear hat is best for you. If AS, then you should probably go for panther.
Most guys in game choose fox hat from what i see. It's also the most versatile one.