Ya, in The Ultimate Fighter 3, Kalib Starnes crushed Mike Stine and made him look horrendous. So in TUF 3 I think I'd lean towards Stine being the worst but Abbadi is a close second.
For The Ultimate Fighter 4, the worst fighter, in my opinion has to be Rich Clementi.
My Favourite Fighters
Georges St. Pierre
Mirko "Cro Cop" Filipovic
Mauricio "Shogun" Rua