What's the best over the counter tooth whitener on the market?

I've seen and heard of the really nice ones by either colgate or crest that have the actual trays with the bleaching product. I'm not sure but I'll have to check it out. What's the best OTC tooth whitener out there (I'm not trying to pay $1000 at my dentist's office...he's good and he's worth it, but not a G)