SMB1 has (mostly) meaty levels and though some are repeated later on, the game itself has stood the annals of time.
SMB2 USA is fun, but not very Mario-ish.
SMB2 j sucks.
SMB3 is Mario bloat defined: quantity over quality, 1 minute levels with poorly thought out design sensibilities.
SMW is SMB3 but good. It's a return to the more meaty levels of SMB1, but with more polish, variety, and substance. A true classic.
SMW2 takes it even further, and is the best 2d Mario game. It has the perfect balance of Mario "bloat". There's a lot of levels, but each one is unique, meaty, and full of surprises and content to last you a while and even tease your brain. Get everything in YI? Guess what? More game. Bow down.
SM64 is a return to SMB3 bloat. Oh great, this level takes me 1 minute to beat. Shit city.
Mario Sunshine is once again, another game that kinda has the Mario "bloat" formula down to a tee. While some levels suck, for the most part, what is there owns and owns hard. Blue coin challenges? Best damn platforming in the series bar none next to what SMG and YI has to offer. The different nozzles on the water pack changes the flow of the platforming and gives power ups an actual use beyond inane novelty's of 2d Mario of old.
NSMB ds. I beat this game in like one sitting on a road trip. Content sparse, and more easy than getting Tauntaun into your bed. Mediocrity incarnate.
SMG. This game makes me want to take my pants off and dance through the streets singing the praises of Nintendo while rubbing myself all over with hot butter.
SMG2 is that pretty girl who is cute, maybe even oinks when she laughs, but she doesn't stand up to that childhood crush you've got with her supple breasts and tender butt cheeks. In other words, SMG is a big hard dick waiting to be stroked and SMG2 is like...a flaccid 3-incher. I mean, it's a dick but it's not THE dick, ya know?
Bonus:
Wario Land - You know how sometimes you can feel that orgasm coming and you're all "this is so good I'm going to do it TWICE, I'm just in the mood for it". Wario Land is like that.