SMB2USA>SMB1>SMB2
SMB2USA is a joy to play, has a lot of replayability using the strengths of the different characters, a lot of variety in the levels, secrets etc.
SMB1 is also a joy to play, but to be honest can feel slightly repetitive so I would not put it over 2USA. I don't find myself going back to play it as much.
SMB2 is a bit mean, and barely has any new assets over SMB1 (I recall the wind, poison mushrooms and the colour swapped red piranha's and that's about it). So the repetitive feeling I get from SMB1 is amped up. It feels more like an expansion pack.