The exact answer is: we don't know. Or to put it another way: it depends. If you had an African lion and a relatively small African tiger the lion might win. It also depends if you mean male or female. There are many other factors. Cats do not normally fight each other in the wild. They spend more energy displaying their prowess and avoiding fights. To test your question scientifically, you would have to get a statistically significant number of lions and tigers and pair them up in a series of controlled fights. Since this is unethical, it is unlikely anyone will ever conduct this experiment, hence we will probably never know the scientific answer to this question. If you simply want an opinion, then at BigCats.com it appears that tigers would win. But that's not science. It's guesswork.