The lowest I can see Sonic being is high B tier, I think he's barely holding onto a spot in A right now considering a lot of the other characters we've seen. There's a lot of mixed feelings on our boy so far, some of his players from Smash4 dropped him, but some faithfuls still remain such as 6WX, Kels and KEN, but if KEN is really considering dropping Sonic as a main like I've heard, and seen based on his twitter, then Sonic might be losing a good chunk of weight. I still want to wait for a few stacked tournament before jumping to conclusions though. ZeRo thinks Sonic is pretty high according to his recent Sonic video, like mid high.
Either way I still don't think he's bad, not at all. I've been exploring other options when it comes to characters, but I doubt I'll replace him, it feels like he's all I know at this point lol. Waiting for Sakurai to fix that Ridley instant kill on Sonic for missing a Homing Attack.