I'm thinking I would go with the tiger.......I'm going to go ahead and concede the fact that both will probably injure me, but at least with a sharp knife I have a chance to inflict some significant damage on the tiger. I'm going to definitely go for poking an eye or two out on either one. I'm going to give him my arm to take the initial bite if I don't find another way to keep him off of me. This way I will have the free hand with the knife to gouge at least one of his eyes, and if he doesn't let go I'm going to give him a severe cut starting from the edge of his mouth to as far up his head as I possibly can. I'm thinking a few of these will most likely make him let go of my (broken?) arm and he will be basically blind. At this point escape is possible. Since I'm on land already my chances are better of getting to a hospital quicker. I'm not a great swimmer, but I can wade my way through water, and that's not comfortable enough for me to have to deal with a blood seeking shark with more teeth than a tiger. There may be more sharks near me too. Standing my ground against the tiger is my best option. I would think a predator would be put off by a human fighting back anyway, and it would turn into a "hey this dude is fighting back" thought process......then if you get a few cuts on him, he'll be more likely to back off.