I'd say these two are probably the most recognizable video game characters ever. Between them who's more popular? I'd say Pikachu since Pokemon is big across multiple mediums including cartoons, toys, trading cards, movies, and so on. 

I feel like mario is definitely a bigger icon in the gaming world. It just has more significance to me. One of my earliest gaming memories is when my brother gave me his old ps1 and told me it came with crash games. I didnt know what that was at the time but when he said it was like mario i got super excited. I dont even remember how i came into contact with mario before that seeing as how that was my first console but mario was recognizable enough for me to get excited. Pikachu might be bigger overall because of all the other media.

Locking! ^_^