I would have to say the best would be in this order.
Hughes: He is the champ and has defended his belt allot.
Bj Penn: Even though I feel GSP is the better fighter over BJ, BJ has at least became champ once.
Then finally GSP, I would normally rank GSP above BJ but GSP , regardless of how awsome he is, he has not touch gold yet, the other two have. We shall see after ufc 65 because if GSP wins, i will throw his ranking way way above BJ.