How about we actually look at this instead of one liners. This is have the most likely Sonic characters that could make it into Brawl.
Shadow: Has a high fan base, seems to be sonic's Rambo or Military man that is willing to get to job done (He is not evil at all, maybe cold hearted, but thats it). Would play like a slidey sonic with ranged attacks and radial blasts.
Knuckles: Large fan base but has had it hit hard by his dumbing down and little character development. Would not be as fast as Sonic but would be able to glide and have strong attacks, probubly like a short Capitan Falcon that "can fly for some reason" (A cookie to whoever gets the reference).
Tails: His fan base has taken some of the most hits becouse of the bad acting after Sonic Adventure 2. Would have his flying ability and also would use machines, he would ether use small hand held machine or use the Mech Tornado 2.
Metal Sonic: Has a decent fan base, but is sometimes forgotten about by some sonic fans. Would play a tad floaty with a lot of stabbing attacks, charging attacks, and a few ranged beam attacks.
Neo Metal Sonic (Lord Metal): Has only appeared in one game but has a decent fan base, some fans of Normal Metal Sonic don't like this version of him. Would probubly play slower than Sonic or Knuckles, maybe close to a mid-fast character, but would be much heavier and a bit floaty. Would probubly have more ranged attacks than Normal Metal Sonic, and also a number of attacks that are indirect (as in not directly coming from him or at a weird angle that may catch people off guard).
Review:
First Pick: Shadow and Knuckles have high chances. Shadow becouse he seems to have the highest fan base next to Sonic and would have some interesting moves. Knuckles has moves that play well into Brawl (Gliding) and would be a fun brawler character.
Second Pick: Metal Sonic/Neo Metal Sonic (Lord Metal) would probubly come after Shadow and Knuckles as he has a decent fan base and move sets, further more Sakurai is looking for more villains in Brawl which dose raise his chances.
Third Pick: Tails sadly hasn't had a good time in the Sonic series, people in generally shy away from tails in favor of other characters. If he appears it will be based on one of his adventure version and play much like them.
Boss: Neo Metal Sonic (Lord Metal) would probubly make the best boss out of all the characters save for Robotnik. He would seem imposing enough for his small size that people would be intimidated by him, and at the same time be able to do some impressive attacks thanks to the ability to reconfigurer his body at will thanks to the fact he is made of Nanites.
You may not agree with all of this, but please give your point and supporting arguments instead of just declaring why I suck (or something similar).