Who is the most powerful big cat in the world?

The tiger. Its bigger and can win almost any fight with the lion. The lions title "king of the beasts" simply comes from its mane being shaped like a crown. That title is not true though believe it or not there's other(but few animals) that could win it in a fight.

Apparently the jaguar has more powerful jaws then a tiger which also allows it to employ a more deadly hunting style.