although i absolutely adore both 2D and 3D mario, my choice would have to be Galaxy-esque games. that game really dazzled and astounded me with it's greatness.
before NSMBWii was showed at E3, my dream was that someday Nintendo would make a new 2D mario... imagine my happiness when they announced NSMBWii! at one point i thought super paper mario was what NSMBWii is now, back then i was so excited for that game too.
thankfully though, nobody has to make this difficult choice... this gen is so amazing in that we get TWO 3D mario's AND a 2D mario too. that's why this gen is THE best gen ever for me. it even has TWO mega Zeldas, what more chould one person ask for??