Melee's are impossible to pick... I would take ROTS Obi-Wan,because he was teh last guy standing at teh end of ROTS, but you can't pick a melee really...
Neither Anakin nor Dooku have ever bested Obi-Wan with a blade though, and i think his defensive style would give him an advantage in a fight with two opponents, who may attack each other if they decide Kenobi is the hardest nut to crack. Anakin would best dooku, but he can't beat obi-wan (that duel has already been fought, so that's pretty conclusive) and if dooku perhaps killed anakin, then there is no evidence dooku could beat Soresu-practicing Obi-wan with a blade. Though he owns him if the fight involves the force...
So.. Obi-Wan is my pick.