Its definitely Jack Bauer... If Jack Bauer were there on the island he would have shot every "Other" in the leg by now to get answers from them... Along with that, he would have broken some part of Ben's anatomy to make him talk and he would have made sure that there would have been no relief for him. AND if Jack was there he would have contacted Chloe already and have gotten a CTU unit on the island, just in enough time to save the world once again from immenent danger... All that in one day... take that Sayid!!!
sayid is awesome and all, but Jack would wreck ANYONE on that island. He'd kill all the others and make a hang glider from their skin and bones and fly off that island. all within-- you guessed it-- 24 hours.