Marth is a beast in Melee; some consider him to be on par with Fox in terms of potential. His disjointed hitboxes, amazing dashdance, huge grab range, and solid speed/decent recovery give him a lot of tools to succeed. It's scary to be cornered at the ledge by a skilled Marth as he's one of the best edgeguarders in the game.
I can't speak for Smash 4 as I rarely play it, but he seems pretty good in that one from the results I've seen. Gotta vote Marth