Sonic Unleashed! I recently replayed it through the Recompiled project and had a wonderful time! It's not perfect by any means, but it's an incredible time!

I personally loved Knuckles Chaotix

Sonic Unleashed

The Sonic SEGA Genesis trilogy, Sonic Unleashed and Sonic Mania

Sonic Heroes :D

good old sonic 2, basically better sonic 1, and not fancy like sonic 3 and knuckle and knuckle and knuckle and knuckle and knuckle and knuckle and knuckle and knuckle and knuckle, only problem is that tails is just either a companion or a skin, he can't fly until sonic 3

Sonic 2 or CD in my opinion

Sonic 1, 2, 3k or Adventure

Sonic U N L E A S H E D (Xbox 360/PS3 version)

Sonic CD. Sonic CD only.

Sonic Adventure 2 is my favourite, then Sonic Adventure, then Sonic the Hedgehog (2006)

sonic 3d games are trash