I bought SMB2 for $20, and was shipped free. I did not like it and sold it for $38 on ebay.
Too many "chance" levels that took the whole gameplay away and made it pure luck if you made it through. Disappointing and not fun.
Then I bought SMB1 for the levels that you are in control of. Still hard but challenging, not stupid like I thought lots of the SMB2 levles were.
I love SMB1, it looks identical, controls the same, and the levels are really cool, unlike SMB2.\
1 disadvantage is SMB1 did not have the mini games as fine tuned (like monkey target and race), but it still has enough to keep you busy.
If you want Monkey ball for the minigames/party games go with 1 and 2, if mostly for the marblemadness levels defintly SMB1