Roy. Yay, more Fire Emblem...
Popularity: Roy is top tier with Smash fan demand. His popularity among players who are hardcore Smash players I don't know so much about. I'm guessing Chrom beats him there, given that FE: Awakening has better sales and is available in the West unlike Roy's game.
Relevancy: His most relevant appearances are about ten years ago (Melee and his FE game). The fact that he's DLC for Awakening doesn't seem that relevant to me. That's not a whole lot stronger evidence than being an AT or regular trophy in Brawl.
Design: Well, we saw his design already. He could certainly be more Luigi-fied. He has a fire theme, so there's a bit they could do with that to further differentiate him from Marth. But still, he's like other FE characters, which makes him not as unique as many other options.
Roster: He'd be returning from Melee, so he has that going for him. He's also not blue-haired, unlike Chrom. Which is nice I guess. Yet another sword-wielding FE lord gets to be a bit like the spacies though (they might play different, but conceptually they're quite similar)
Sakurai knowledge: Roy was intended to be in Brawl, and Sakurai has said that he doesn't like cuts. Sakurai could see putting him back in as a way to rectify that. Or he might decide what's done is done and leave him out. Who knows?
Competition: As I mentioned before, the main FE characters are all quite similar. Which is why I doubt we'll see four of them (in addition to Fire Emblem not having huge sales), so there's a very good chance he's competing for just one spot against Chrom and Lucina.
Roy chances: 43%
I think he has the best chances out of the FE crew, mostly because of the fact that he nearly tops the fan demand list in both Japan and the West. He also has more unique move set potential than some other FE options.
Roy want: 30%
I don't particularly want any more FE sword-wielders, but Roy gets more points for having the fire gimmick to make his move set more interesting. My want will be even lower for Chrom and other FE characters similar.
Another reason I'm not excited about FE sword-wielders is that there are deserving characters from other series that are also male sword-wielders (Shulk and Isaac, for example), and so there's some stepping on toes there.
Mii prediction: 60%
There are people who believe the "leak" (even though it was 50% wrong about E3). But there are also people who think that Wii Fit Trainer fills the kind of role Mii would have or that Smash doesn't fit the image Nintendo would like to maintain for Miis. But Miis are kinda everywhere, so I think most people will think they have a decent chance of appearing.
Nominations:
Simon Belmont x5
Smash Bros representation for series has never been solely a popularity contest (except for third party characters, but those weren't series but individuals) and has never been.
I'm pretty sure popularity plays a pretty large part. Why do you think Sakurai took a poll in the first place? Sakurai said he was considering information about fan desires for this game as well.
It's not the ONLY consideration, and in all the games he gave a couple slots to characters that comparatively little modern popularity/fan desire. Roy can also count considering his game hadn't been released yet. Wii Fit Trainer fits into that mold as well.
The most popular and famous characters are already in the game, so it will be less of a factor this time around, I think. But there's a reason the most popular characters are already all in, and it isn't because popularity is irrelevant.