No zipper (slip-on):
Chose this opton if you want a fast to remove and put on head. This is also a good choice for new fursuiters or for someone who overheats easaly.
zipper:
Chosing a zipper will give you a more snug fit and slimmer looking head especaly around the neck. The zipper should be on whatever side is easiest for you or down the midle.