Your question cannot be answered with the information currently available.
"More Famous" is too idiomatic for anyone to provide an adequate answer without poll data from various areas & age groups, perhaps even from different socio economic groups.
Without any data of this sort there is no way to really determine which person is more widely known to the general populace therefore any answer would really be speculation, opinion and/or conjecture from the individual who answered.
I guess its Usain Bolt because he has got more attention since the 2008 Olympics. But Dolly Parton still remains famous.
usain bolt
usain bolt
Usain Bolt
usain bolt is more famous
usain bolt
usain bolt
usain Bolt
Usain bolt
it is Usain Bolt
Usain Bolt
Usain bolt
usain bolt