The newest Sonic I've played is Sonic Adventures on the Dreamcast, so I can't say anything about the new games. However, I love the old games. I grew up with Sonic 1 and 2. Those 2 games made the genesis my go to console for a long time, along with Rocket Knight Adventures but I digress. I got Sonic 3 & Knuckles sometime later and find it to be a very good improvement to the series. However, the best Sonic game I've played is Sonic CD in all of its pixelated glory. If Adventures is anything to go by, I doubt I'll play a better Sonic game.
Also:
[media=]http://www.youtube.com/watch?v=LJXKoubh9sQ[/media]