So long as it’s Nintendo’s Mario, 2D, and fits firmly into the platforms genre, it’s a valid response here.

So what’s your favourite? Personally I have a major soft spot for New Super Mario Bros. Wii. It took me AGES to complete for the first time, and finally getting 100% was a great accomplishment for me. Unfortunately, having done that there’s not much else to do, but it’s still a great game anyhow.
Also the soundtrack slaps.

The original New Super Mario Bros. on DS is also excellent, and I love the end credits theme.

New Super Mario Bros U (I’ve only played the Deluxe version) is good, but not worth the full price. To think I originally got BotW because it took less space on my Wii U…
I do miss the total cheese that is Wii’s item system, though.
All the areas felt samey, though. The continuous world (and only slightly modified music theme) was a mistake, especially because it can trap you with hazards since you can’t just change world to get out.

Super Mario Bros. Wonder is good, but too short. It feels like it would introduce a mechanic and then hardly use it. Not bad, really quite good fun, just needed extension.

I’ve played Super Mario World on both Switch Online and an SNES (only game I have for it lol). Switch responds better and allows saving, but SNES feels more authentic, though the controllers are a tad worn. Too slippery and different feeling in terms of handling, much less forgiving than newer games despite apparently being considering piss-easy. I just suck at video games.
Not being able to save on SNES except after castles (and maybe a few other situations? Can’t remember) sucks, especially having to trek back to the first area every time to farm lives since they reset to five when the system turns off. The furthest I’ve gotten is just past the forest of illusion iirc, assuming I’m getting the name right.
Also I think the cartridge sometimes failed to store save data and wiped files. It’s been a while, who knows if mine’s still there? It is over 30 years old, after all.

I’ve played the OG Super Mario Bros. on an off brand bootleg famiclone thing, and on Switch Online (original on NES library and All Stars on SNES library). Not my favourite but not terrible.

Have played Super Mario Bros. 3 on Wii U virtual Console and Switch Online, but I think only the All Stars version on Switch. Too hard imo, I suck too much.

I think that’s everything…

Oh, right, and New Super Mario Bros. 2. Alright game, but if you somehow see the game over screen you’re a threat to the gene pool. I don’t even know how you COULD see it unless you deliberately commit suicide many times at the beginning of a save.
Lives are endlessly abundant, no matter how much you may die.
I don’t think I ever beat the final boss without the “you suck” pity powerup you get if you did enough times. Again, I suck.
Reused soundtrack from Wii is good tho.