Classic Sonic: He has a bigger head than normal, i made his quills more like straight lines, to show how he isn't fully developed yet.

Adventure Sonic: He has really round quills because they're midway through development, his body is bigger and taller to fit his head size. His body is also slim.

Modern Sonic: His body is completely developed, his quills are normal: not too straight and not too round. His shoes are now bigger and have the buckle, he is also slightly taller. Now he has an atletic body, because it's fully developed and (obviously) because he fights and runs a lot.

I'll load the other arts later. Because for some reason i can't post them now.

Here's the Adventure Sonic Model.

Here's Modern Sonic.

You have to wait a while (about 5 minutes) to post another image. It's a glitch on this part of Fandom for some weird reason.

Anyway, with your art, you did a superb job capturing Sonic's adventurous personality.

I also forgot to point out that the blue gets stronger

Neat detail to add to your design of Sonic.