Your question cannot be answered with the information currently available.
"More Famous" is too idiomatic 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.
Justin Bieber
Justin Bieber is more famous because not all the teenagers today know Shania Twain.
You choose! I think Justin Beiber but it is your choice!
justin bebier
Michael Jordon of course you noobs
Justin Bieber is more famous
justin bieber is more famous
I believe Justin Bieber is more famous.
Justin Bieber
Justin Bieber.
Justin Bieber.
justin bieber
justin bieber
Justin Bieber
Justin Bieber
Justin Bieber
Justin Bieber, he has more fans.