A good way to check things like this is googling the name and seeing how many results come up. Who has a bigger presence on the internet is a good comparison to who has a bigger presence in general.
Mario: 642 million hits (Super Mario has 272 million if you want to be stingy, but really, when you google Mario he's the only one that comes up)
Pikachu: 31 million hits.
It's not a contest.
And just for giggles, here's some other famous video game characters:
Mega Man: 306 million (but, one does need to keep in mind the generalness of those words could mean a lot of other results, although the first page is all Mega Man)
Pac-Man: 130 million
Master Chief: 124 million (same problem as Mega Man though)
Luigi: 123 million
Zelda: 71 million hits (No real way to check Link as his name is a word, and bear in mind some of these undoubtedly refer to Zelda Fitzgerald)
Kirby: 66 million (again, other Kirbys exist)
Yoshi: 32 million
Sonic the Hedgehog: 23 million hits (just 'Sonic' is 231 million, but in fairness, the first result is the burger franchise)
Donkey Kong: 23 million hits
Bowser: 15 million
Lara Croft: 15 million
Nathan Drake: 14 million
Solid Snake: 13 million
Samus: 6 million
Ganon: 5 million
