Mario is the best suited for Nintendo's mascot. I don't really see why so many people think Link should be it, no offense to those people who chose Zelda in the poll.
Mario is Mr. Nintendo. You used to see his face on the back of every instruction booklet you got when you bought a new game. I'm pretty sure if you were to take the instruction booklet of, say, Ocarina of Time or Majora's Mask, and look at the back, you'd see Mario's face. I wouldn't know since I don't have those instruction booklets, but I still have a few N64 games' instruction booklets, and sure enough, he was on there. One of those was Pokemon Stadium, so there's no doubt in my mind that he's on the back of Ocarina of Time and Majora's Mask's instruction booklets.
Mario also has great games. The Super Mario Bros. series is the longest running one. He's also had many other games in other styles. Other series in Mario are Paper Mario, which I think we can fit Super Mario RPG: Legend of the Seven Stars with that series, and Mario & Luigi, those two series being RPGs. His series was also the one of first to go 3D, and those games were fun, and still are fun to play today.
Last but not least, his spin-offs. Even though I hate them all, except for the Mario Kart series, it shows just how versatile he is. Mario can play soccer, he can play baseball, he can race, he can hold parties that get repetitive, yet people still buy them. I'm not one for spin-offs for Mario since I just don't like them anymore, but they prove why he's a better choice in mascot for Nintendo.