Originally Posted by Starmud
The thumbs are slower than the fingers, I wouldn't recommend using them.
You'd think so. In my case they're not. I can't button mash with my fingers as i just lose my momentum and composure. With my thumb i can keep it constant and still.
Saying using fingers though, one way my brother does it is to press his index and middle fingers together and then slide them rapidly over the button. Works for him but does cause a blister after a while.