i always do over. this girl i was dating did it under. when i asked why, she gave a very good explanation:

little kids like to swat at things like that & if it rolls off the top, then they will unroll the whole thing, but if it comes off the bottom, then when they hit it, it just spins around w/out coming off the roll.

makes perfect sense to me, but that doesn't mean that every time i went over there i didn't fight the urge to switch it :lol: