Well, because the Mario series is awesome everyone's always asking what other people's favourite games are, so let's be a bit more controversial. What's your least favourite Mario game?
And to be even more so, what's your least favourite non spinoff Mario game too?
For myself, my least favourite mainstream Mario game is probably Super Mario Land. It looks terrible, has aged poorly, has mediocre controls and physics and hardly any content with only 12 levels.
I know some people are going to complain, but of all the "Main series" games my least favorite is Super Mario Sunshine. Don't get me wrong, I love this game. I just don't like it as much as the others. I mean I never played Yoshi's Island, Super Mario Land or SML 2, The Lost Levels, Galaxy 2, or 3DS Land. So I have to go with SMS, which is just the weakest one to me. Even though I rate the game an 7 of 10.