Top 3 I want in;
Brian (Quest 64) - I won't pretend he has a real chance even then. It's not so much being from an obscure game as that THQ abandoned it by now, and it wouldn't be worth relicensing due to this. If it got bought out and revived later, a chance is remotely possible. Won't stop me from supporting him.
Fulgore (Killer Instinct) - One of my top favorite fighting games and he's also the mascot. It didn't just define combos, but it's why we got announcer chatter as well. Arguably it's what started the idea of Counter-like moves, but I can't prove that one.
Rabbids (Rabbid franchise) - I was hard-pressed for a 3rd one, but I admit this is a big deal to me. I love these guys. I bought their latest Burger King toys, have the excellent Mario crossover game. I've seen a bit of the show. They're funny(and came before the Minions, so aren't Gaming's Minions. It's more like Minions are Movies' Rabbids), have tons of capabilities, great costume options, and have a pretty great voice, imo.
(Runner ups would be Slime and Agumon, respectively. I do want them in, but I have less hope for 'em in comparison. That said, Slime is the de facto iconic Enemy overall and full of tons of moveset potential. Agumon is from an iconic monster raising franchise, and full of moveset potential too, having over 20 ways to evolve and become fun). Steve and Master Chief are also notable additions, though Fulgore obviously beats them for me among Microsoft options. Even then, they're all good options.
...Actually saying who I don't want is kind of impossible. I'm fine with anyone being in. Though that said, some of the ones I'm less interested in are Luminary(I like Erdrick and the original DQ1 hero a bit, but I would rather have the more iconic option in the long run. They're still cool choices), Rayman(I never got into the games He's a cool character, though). Banjo & Kazooie are cool characters, but the games did nothing for me whatsoever. I just don't have a seething hatred for any character. I don't see a point in being angry over anyone getting in. It seems silly to me and accomplishes nothing.