I vote for Super Mario Brothers. I think the game play and the controls in SMB were just a little tighter than Super Mario Brothers 2. SMB2 always seemed too floaty and slippery to me. SMB just has more classic platforming moments than SMB2 as well.
While Super Mario Brothers was not the first game I ever played and enjoyed (that award goes to Dig Dug), it was the first game that showed me how "magical" gaming can be. Seriously, I hate to use the word magic but SMB just had it in spades. Half of my childhood memories involve playing Super Mario Brothers with all my friends...I remember how overjoyed I was every time I beat a single level. I remember how confused I was when I got to Bowser's final castle. I remember calling my friends on the phone and discussing with them how to actually get to the end of it. So, I guess that was the first time I ever got lost in a game as well. Then when I actually beat the game it felt like it was the greatest achievement of my 6 year old life. After my experiences with SMB, SMB2 can not possibly hold up to SMB.
However, this being said, the one major thing I admire about Super Mario Brothers 2 is its vision. I love being able to play as Luigi, Toad, and the Princess. I also liked all the villains. I believe Super Mario Brothers 2 had the best world and the best villains in any Mario game. I always remember the battles against Wart, Fry Guy, Mouser, that Giant Crab boss in world 5, the shy guys, those masks that chased you when you had a key, the albatrosses, the pink thingy that spit eggs at the end of each level... uhh...and everything else :) Super Mario Brothers 2 was wonderful for its vision alone...even if the control and over all platforming was not quite as tight as SMB. SO, I have said it before and I will say it again...I would like to see some of these characters come back in a future Mario game. Its sad to see that Wart, Fry Guy, and Mouser just fell off the face of the earth after becoming cartoon stars. I wouldn't even mind seeing some of these characters in like Mario Kart, Mario Tennis, or Mario Golf. It can't really hurt...
Back to the point though...I take SMB over SMB2. However, if you are asking for my favorite Mario game I will say neither 1 nor 2 because Super Mario Brothers 3 is by far the best in the series.
