Best- One that's not so damn repetitive.
Worst- One that's always doing the same move and has a low amount of variety.
Examples:
Best- Mario, Dr. Mario, DK, Bowser. They don't spam too much unless you are at range.
Worst- Ganondorf (Spams ^B when you jump and spams B & >B), CF (A,A,A..), Fox & Falco (B,B,A,A,A,A), and mass grabbers(Link, Marth, Roy, Samus, etc.)
It's been a while, hasn't it?