For me its between Mario and SmashBros. I could never decide. I'd say Mario because Mario turned me into a full time gamer when I was a kid and he's my favorite videogame character of all time. Mario 64 blew my mind when I was young as well. Then I'd say SmashBros. Because out of any game series I've ever played, SmashBros. is the game that I've spent the most time playing and it's been the game that I'm dedicated to the most. SmashBros. for me gave me the most happiest moments in gaming. It has everything I love about Nintendo. It's also the best game to order pizza and call over about 10 friends and have a blast. Really more me,it's to tough for me to ever choose between the two.
Donkey Kong for me. Mostly due to the Country series. Just wonderful games really. It's hard to pick just one series but I just have fond memories of all the DKC titles.
It's a tie between Zelda and Mario for me, but I voted Mario since I've been playing it all my life and the very first video game I played was Super Mario World 3.
So yeah, gotta give it to the chubby plumber in red, he's what originally got me into video games.
I can't believe Animal Crossing isn't all this list. I would definitely go with AC. It may not be a "legend" or anything like Mario and Zelda are, but ever since I played the first AC I couldn't put it down. The series is phenomenal. I think that the first one was the best though, and I really hope the 3DS version keeps a lot of the features the first one had. To me, the last two really kind of tried too hard.
If I had to go with one of the "original" type of series that came out years ago, then yes I would go with Mario. I never really could get into Zelda, but Mario is still awesome even on the 3DS after all these years. I played it ever since I was a little kid, and so when it comes to the old-school type of series then Mario will be my favorite.
I used to always go with Metroid on this since the Prime games were so immersive and atmospheric, and while nobody seemed to like Other M I loved the acrobatic, cinematic gameplay style and I wish I could see more of it. But now that I've played through Skyward Sword I'm not sure whether I prefer Metroid or Zelda.
All these series rock, but I think I have to be unoriginal and say Mario's my favorite. When I discovered him on the Game Boy when I was younger, that's what really kickstarted my love for video games. Now I think I've played every Mario game in the main series, and a buttload of others too.
It's tough, but first game was Super Mario World and I love Mario games since that first day! I learned to love Zelda and Pokemon along the way, but Mario was first.