Marth in Sm4sh has been toned down really hard compared to his Melee counterpart. He's a bit more laggy and a lot of fundamentals and mechanics in Melee for Marth aren't present in Sm4sh. Such as the Ken Combo (seen someone do it before though) and the safe double f-air in air.
I'm not much of a Melee know about but imo Marth was nerfed for a huge chunk in Sm4sh but imo he's still pretty viable after all the patches even if it still doesn't feel like his godly spacing game in Melee. Though, that's only if you can play him right.
However, when compared to Roy: Roy seems more favored to me cause of his insane power and fast moves and ironically, him being better close up. Marth isn't that fast like he was in Melee and in Sm4sh you gotta make every hit count.
All in all, whatever you prefer more can still get you a win.