Tigers are bigger, faster and stronger. THey also have longer claws. Lions generally also hunt in packs. Tigers are more independent. The only thing that gives the Lion what might be an edge is their mane. The lions mane would make it difficult for the Tiger to reach the Lions throat. Big cats generally always target the throat of their prey. The tigers strength may be enough to topple a Lion, but it all hinges on the Lions mane
this is what youtube is for. seems the tiger has the upper hand.
http://youtube.com/watch?v=Qx00Ne-M9M4&feature=related
in other news, tiger also beats crocodile.
http://youtube.com/watch?v=pGe6GP4lALU
and in a less surprising revalation: sled dog doesnt stand a chance against polar bear.