If you mean currently, then Anand, certainly. There are several other strong contenders right now, too, but not Kasparov. Garry hasn't played seriously in more than three years, and he's 45...
If you mean ever, then Fischer...
Who?
Sort:
I think it's Cheater_1 
Who do you think is the strongest chess player?
The rated 2800+ Anand??
O r do people still support Kasparov?
Who do YOU think?