I won't say definitively until I've played them all. I've played only the classic Sonic games, up to 3D Heroes. I'm still of the opinion the Sonic Adventure has held up, and is still fairly good even though it's a little jank. I didn't care as much for Heroes, as it was super janky. However, the best I've played are the original trilogy. I know there are plenty of 3D games not well regarded, but in recent years Sonic games have not been a critical failure as some were in the past. I think some of the modern games look quite good from the gameplay, and tend to mix elements of 2D and 3D. Depends on who you ask, some say they are good, some say they are trash. I personally don't see how they could be trash, given most of them look good just to watch.
Hating Sonic has become a meme at this point, and given all the jaded negativity that a lot of games today face, I don't put much stock into what's said about the franchise.