The original SMB was too frustrating. There were too many parts that were a matter of pure luck rather than skill (those stupid maze levels for example). And the control was terrible; it got way better in the later games. I don't know what age-group that game was released for, but it was way too hard too. Not nearly enough 1-UPs, and near the end when Bowser shoots a continual stream of hammers at you, it's not even fair.
SMB2 was OK, but really started getting old after the first couple levels. Not to mention that there are only two characters who are actually usable (Luigi and Toad; Princess was slow and sucky, and Mario was just worthless in every category). SMB2 was fun when I put in the Game Genie code to let the mushroom guy jump higher than Luigi though. Some levels were really amusing too, like the one where you have to jump across the waterfalls by landing on fishes. I liked the long levels with more than one route to take too, and I like the bomb guys. But I hate the desert. Oh, how I hate the desert. The desert ruined the game.
SMB3 was so long it hurt my brain, but the levels were nice, the control was nice, and all the levels were very beatable, even when they were hard the first time you saw them. There were enough secret things in the game to keep you entertained too, like the coin ship and the N-spades and the hidden suits and suchlike. But any game that long without a Save option = bad, to me. Maybe this was just before the era where savegames appeared in every single game released, but oh well. It also was way too easy. After you collect up 15 P-Wings and have 157 lives and can use those cloud-things to skip half the levels anyways, it's a tedious certainty that you'll beat the game eventually if you throw enough tries/lives at it. The game was fun when I put in a Game Genie code to stay permanently as HammerBrother Mario, and so I could continually jump in mid-air though.
So in summary, I vote for Duck Hunt. *does so*
