Roy was worse than Marth in every way possible. Its like choosing Pichu (worst character in the game) over Pikachu (still pretty bad, but playable), except that Marth is god tier and Roy is like lower-mid, which is an even bigger difference.
It all depends on who is playing. With Roy, I
always win, at least against friends(I don't play tournaments). But with Marth, I hardly even win. I suck as quick characters, and that is what Marth is. Roy, on the other hand, is slower, but much more powerful. I'm better at that.