Fire Emblem is one of the harder franchises to choose characters from, in my opinion. First of all, all the games USUALLY sport different heroes, with exceptions when remakes and sequels are made for very few games. Some end up tying in together in later games, too, but sometimes the focus shifts from one hero to another. Ultimately, Fire Emblem seems more like a popularity contest between the lords, with the exception of Marth, the one who started it all.
The next problem is that lots of popular FE lords use swords. Not all, but lots. I know that one problem some people have is the addition of more characters who use swords, having seen opinions elsewhere where people go "This ain't Soul Calibur!", also citing that sword wielding heroes are kind of cliche. A counterargument to that is that some of the greatest heroic representations are sword-wielding heroes.
My support still goes for Lyn or the Heroes of Elibe. I'm sure I WOULD have voted for Micaiah for the sake of A) Avoiding a sword wielder and B)Avoiding this 3 character thing that seems to popping up (and which I kinda support), had I more knowledge on her, but I don't know that much about her. How popular is she? I never played the Wii FE games. What attacks does she use? How does she act? Sell her to me! xD I am also willing to bet that there aren't many other main characters that use magic. :/
One other small SMALL case against Micaiah is the fact that she and Ike stem from the same part of the Fire Emblem universe, but if one were to make that arguement, the same can be said about having the Heroes of Elibe as one character. In fact, in that case it would be a much stronger argument, because there is a third character from that part of the FE universe.
It is REALLY hard for me to decide who deserves the most support. I just have a bias for the Elibe trio because they are from the game in the series I actually have, the first international release. I'm trying my best to show some objective criticism on several sides, though, so let me wrap up:
Micky: She's a magic user, a girl, a main character, that's a plus! At the same time, is she well liked? Are her abilities cool? Will she combat with Zelda's regular form for the title of "girliest magic user"?
Elibe dudes(and dudette): Pretty awesome lord representation with potential for a bow wielding sword wielder, an axe wielder, and a horse-riding sword/javelin wielder. The con is that that's TWO sword wielders, three characters from the same game, and a rip-off of Pokemon Trainer.
Lyn alone: A lady, an FE lord, kinda looks like Marth and Zero Suit Samus fell in a blender with some green food coloring. The bad news is it's another sword wielder. There are ways to make sword wielders unique, though. Lyn can be samurai style, Marth can be prissy prince style, and Link can be... Link style. Of course!
Ponder them thoughts and discuss!