I’ll start - I actually quite enjoyed Sonic 06, despite the bugs and long loading screens. I may be biased because I’m a huge Silver fan but I actually also really like the gameplay with the stories focusing on their main characters, but occasionally intersecting and having sections with their supporting characters. It had huge potential, but as we all know, it was unfortunately quite rushed. I think, in my very non-critical views, that it deserved a better chance.
Mario 64 is definitely the more polished game.
However, the different play styles, repurposed levels, story, open world exploration, etc. make it more fun to return to Sonic Adventures over Mario 64 in my opinion. There is certainly a lot of jank, but that era was pretty much defined by jank.
That being said, I think the N64 era holds up the worst for Nintendo. I tend to prefer SNES or GameCube games over most N64 games, so I’m probably biased.