Any character can be made unique, especially in the smash bros games. You don't need to be a fighter for that to happen (and in many cases it can make the character more interesting). At that point, you need to look at which characters are more important, because if you're just looking for characters with unique gameplay, then you're probably being a bit closed minded on how a character can be added.
Toad has been in the series ever since Super Mario Bros. 1. However, he's only really playable in Mario 2, Spinoffs, and a few of the more recent games. Every other time he acts as an item giver/information giver. I find Toad boring, but I can see why people want him in. Especially over Rosalina, while I prefer her because of a lot of things, she's much more recent, and I'm not sure how important she will be (we'll have to wait a few more games before we see if she's important).