I belive that Super Mario has proven to be the "face" of nintendo, not necessarily because it's better, but because it was FIRST. nintendo's first game was (duh) Super Mario Bros. the classic. then came SMB 2, then SMB 3, then the Super Nintendo came along with Yoshi's Island a.k.a. SMB 4. N64 came out all those years later with 3-D, then came one of the most memorable mario games from my childhood, Super Mario 64, come on, who didn't like swinging bowser around by his tail? When Super Mario Sunshine came out on the Nintendo Gamecube it had Mario, Peach and all the toads taking a vacation, a very well thought out game but no one considered this game a TRUE sequel to Super Mario 64.
COMING FROM A FAR AWAY GALAXY...yeah you know whats coming...SMG (no not the gun) 1 & 2. These have proven to be some of the best games of ALL time, what with the gravity switching, black holes, and who knows what else, and in SMG 2 here came yoshi! he had his own power-ups such as, the balloon fruit, the bulb fruit and the red hot chili pepper! several more power-ups made an appearence than the previous game such as, the drill mushroom, the cloud flower, and the boulder mushroom, and coming back from the previous game were items like the fire flower, and the spring mushroom and who didn't like turning into a bee or a ghost? that was fun!
Now think ALL the way back to SMB 4 (yoshi's island) after that, there was a yoshi's island done on the GBA, and later on the DS, they featured baby mario, a reasonable game, then there was New Super Mario Bros. on the DS but there was no original mario side scroller since SMB 4, until now...out of the blue with almost no warning nintendo releases NEW super mario bros. WII!!!! I think this was like the BEST side-scrolling mario games nintendo ever made in my opinion, mostly because you could play with 3 other people SIMULTANEOUSLY, and either play competitively trying to kill each other, or play cooperatively, and try to finish the level by helping each other. the best, or worst part (depending on if your good or bad at the game) of competitive play was the poison levels, or the lava levels, where it was too easy to get killed by yourself let alone with people out to kill you.
All in all mario has become the face of nintendo, 1. because it was first, 2. because it has more games, and three because it's just how nintendo rolls. Thats what I think, please read it, I pulled a shoulder muscle typing this, be greatful! hahahaha