Sonic, without a doubt, should not be in Brawl.
Also, I think I prefer Young Link over Toon Link, simply because Young Link is from Ocarina of TIme, which is the very video game that got me into games.
As for the characters that should be in otherwise, I made a list...
In no particular order:
1. Lloyd, Tales of Symphonia
2. King K. Rool, Donkey Kong 64
3. Eddie, Iron Maiden(How cool would that be?)
4. WALL-E, WALL-E(To rival ROB)
5. Majora's Mask, Legend of Zelda Majora's Mask(The final boss form)