Which is more famous Sonic the Hedgehog or Harry Potter

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.