The Werehog WAS a dumb idea, but I don't think it fits here. It may be Sonic, but it's not Sonic's natural form. If your going to include the Werehog, you should include all Super Sonics, Hyper Sonic, Darkspine Sonic and Golden Knight Sonic as well. :P
Sonic started to lose his looks after Sonic CD. NiGHTS was probably partially to blame- they accentuated his spikes, giving him a harlequin look. They also started to make him skinnier than the satisying sprite of old. The older version are balanced just right in proportions to convincingly look like a round ball when spinning. Compare the very first shot of Sonic finger waving on the first Sonic the hedgehog, a look of assured confidence on his face, to the gaunt gangster wannabe of later incarnations.
From the 2D Sonics, yeah, Sonic 2 FTW. Though Sonic SSBB is also one of my favorites, especially for the 2.5D perspective. My favotire 3D Sonic has to be Sonic Adventure 2 Battle when you have all the items. I just think he looks so awesome when he's all blinged out like that. That's also the First sonic game i've ever played.