I think you need more practice with your Sonic. First off it seems as if you use his forward+b and his down smash a lot. His neutral+b can be used to lock onto opponents and then you could probably combo from there. Just try to mix it up a little more, that way you'll be less predictable. It also seems as if you don't know how to short hop. I don't know how to on the other controllers, but on the Gamecube controllers you just have to tap X or Y. You COULD also use the control stick but that's much harder.
As for which moves you should use more often, try his forward air, down throw, and maybe his dash attack for racking up damage. And then to finish, use his forward smash or his back air. Those are probably the only two moves that KO someone at around 120-150%.
Sorry for the long post but hopefully this will help you improve your Sonic.