Sorry people, but I won't be going in for this sort of hype.
My vote will be for Pelé, but even within tennis Andy's a long way behind Boris Becker, or even Rafa Nadal, with regard to teenage talent. Doesn't mean Andy can't go on to be the greatest ever tennis player (we can dream), but let's have a reality check.
Also, I probably don't want him catagorised as a brilliant teenager, most of them go on to do relatively little in the future (the likes of Pelé and Becker being exceptions)