Sonic 1, 2, CD, 3 and Knuckles are still the best Sonic games. They were made in the early 1990's. Sonic started to go downhill with 3D Blast and later 3D games. The camera is always an issue with 3D Sonic games.
Sonic CD is probably my favorite Sonic game, the levels and music are amazing. I've played later Sonic games and none are as good as the earliest ones. Sonic 4 and Sonic Generations are 2D and good games, but still not as great as the earliest games.
I heard Sonic Mania is a good game and it's 2D, but I've never played it. I would highly recommend Sonic Origins since it collects the earliest Sonic games and they are still the best in the series.
Sonic CD is probably my favorite Sonic game, the levels and music are amazing. I've played later Sonic games and none are as good as the earliest ones. Sonic 4 and Sonic Generations are 2D and good games, but still not as great as the earliest games.
I heard Sonic Mania is a good game and it's 2D, but I've never played it. I would highly recommend Sonic Origins since it collects the earliest Sonic games and they are still the best in the series.