Best Marth - Why you ask? First of all, his are fast and well paced and puts good pressure on your opponent. Has also good air attacks, including his meteor smash.
Second would be his counter move, i'm a master with its counter, especially when my opponent is under pressure. Only this fails...
My best is marth. for some reason ever since melee, he has been my best. he's quick, can deliver good damage and final blows, and especialy, his counter is fast. It required some practice to make good use of the counter. especialy when your opponent never expects it or when everyone is beating...