We separate our favorite Marios into 2d and 3d.

For 2d, it's Super Mario Bros 3. The levels are bite sized and there's lots of them. It's very easy to beat the game in a single sitting or play through all the levels across multiple sittings (if you're playing on Mario All-Stars [which we usually do because we had it as a kid]). The powerups are all really cool and the physics feel very nice. We've never liked SMW's physics.

As for 3d, it's a little more difficult, but we think it's Super Mario 3D World Deluxe. We're always going back and forth between this and Super Mario 64, but 3D World Deluxe is probably always going to end up winning because it's just such a joy. It's beautiful, it's sleek, the movement is really fun (especially with the new moves added in Deluxe), and Bowser's Fury is so fucking good. We've been hoping since that came out that the next full 3D Mario was going to be similar to Bowser's Fury in the way that it's kind of a single open world thing.