Well, I think the match-up for Mario vs Sonic is still 60-40 in Mario's favor with the edge going to Mario in terms of edge-guarding Sonic and preventing himself from being edge-guarded.
How about we discuss the Sonic match-ups with the new additions like Samus?
Also, Tero. Sonic is 10x better than what he was in 2.6, so stop trying to ask the PMBR to make him Brawl MK broken like he was in 2.1 and 2.5. He has more killpower and more aerial momentum to help chase his combo'd opponents now which is what he needed.
Actually, I keep hearing around the Sonic boards that Sonic is the only bad match-up for Fox; like it's 55-45 or 60-40 in Sonic's favor. The trick is mastering on dragging your opponents across the stage with Side B, Jump Cancel, and then Side B again. There's also the Blast Attack to set them up for stronger hits like Fair or Nair. Fox's Neutral Game is pretty strong, but Sonic can play the whole Dash Dance/Wave Dash movement better than Fox. If the problem is that you keep getting trapped in your shield by Shine to Nair pressure, then you gotta buffer a roll away from Fox.
As for Falco, I am not sure. I know that the Side B Jump Canceling technique is very useful for all three spacies. Whether you lead it into another Side B, a Jump Canceled Grab, or maybe even a FSmash. I hope this helps you a little bit.