1) Ice Plains/Ice Plains Spikes (i'm in the minority in that i like ice levels in mario games, and these biomes really give off those vibes. the ice theme from smg plays in my head when i think of the spikes in particular. also snowfall is really nice and rooms made of snow/ice look lovely)
2) Mesa (so colorful and variable, it's always a pretty sight, shame about the nerf though)
3) Extreme Hills (they can make for some really breathtaking scenery and landscapes with their insane generation)
4) Cold Taiga (snowy forest aesthetic)
5) Mushroom Island (i just really like the uniqueness of the biome, and mooshrooms are cute)
6) Flower Forest (they're really pretty to look at actually, all the colorful flowers)
7) Roofed Forest (like tb said, the grass is a really nice shade of green, and i like the look of dark oaks. plus mansions are fun)
8) Savanna M (similar to extreme hills, but more... extreme. its just so weird being in a flat savanna and suddenly fucking 255m mountains lol)
9) Forest (always feels tranquil in plain forests, they're nice places to be. wolves are adorable too)
10) Mega Taiga (moss stone is fuckin baller and also giant spruces are great sources of wood, not really a fan of how podzol looks though tbh)