I find the cheap see threw rubber ones suck and always fall out and you cant even talk with it.
you can't get any better than the ones a dentist makes you but other than that I like Shock Doctors
My vote for best mouth piece is Dougie
I hear Dougie uses a mouth full of oatmeal as a mouth piece.
Go to the dentist. They will form fit it to your teeth. Sticks to your teeth really well.
I iz da champ baybee! I am currently in talks with Quaker Oats as my sponsor.
P.S. - I like http://www.wipss.com/