If I may throw my own lot in. I would have to say Sonic can be a rather aggressive character depending on your own style and creativity.
To elaborate, as an aggressive Sonic player your goal is to never allow the enemy to breathe. To constantly switch between spin-dashes, blast attacks, and of course the very useful jump canceled grabs. You don't carry a great deal of power but your moves are fast, link into each other well, an cause efficient shield pressure. An with Sonic's speed you can literally overwhelm the opponent long before they get a chance to stable themselves.
Yet that's just my take on it, nothings better than field experience. So pick up Sonic and give it a shot see how you like it.