Going strictly based on "one per class" feels a bit too lenient. Ok, yes, there's a case for ranking Mordecai, but I can't see ranking Mordecai above Lethe, since they both have the same amount of plot, and all that (and then Ranulf beats both of them in plot pretty handedly, especially when you consider FE10.)
I think its easier to mesh all Laguz into one category, since really, the only true difference about them in the DL is their weaknesses. They're all one dimensional with a niche (transformation aspect), and frankly, they aren't very interesting at that, ranking more than one feels meh.
In general, equating Laguz to Beorc just doesn't sit well with me. Feels like we should limit ourselves to one Laguz (Ranulf works) that isn't a Royal (of the Royals, as seems to be popular consensus, Tibarn's a good rank, Naesala's worse, but still not a bad one, and no one care about Giffca.)
So...yeah, when saying "class representative" I was referring solely to Beorc. The "one per class" aspect was merely tossed in cause it stops some of the FE Dueler Syndrom. Largo would be an exception as I can't see myself ranking him at all, despite the unique class. Forgettable character, and to rank him over Callil would be awkward, and Callil's not exactly a good idea at that.
Other Exception is Oscar/Titania for Paladins. Paladins are the most common class in the game (6 total), followed by Sages (5), and then Swordmasters (4). So by ranking two of them, it reflects this aspect! Though, real reason would be that Titania is one of the primary plot figures, and Oscar's one of the most widely used characters (gotten in the first chapter, and solid the whole way through unless you are RNG screwed), and has a decent number of scenes in the first 1/3rd of the game.
So what was the point of all this rambling? I don't know. Mostly just thinking that "from a class that isn't ranked!" is not a reason to rank someone based on that alone, HOWEVER, it does add a point to their favor.
Of the Beorc who are popular for ranking so far? Greil Mercs barring Titania/Oscar which I covered all are different classes...well, Shinon/Rolf, but Shinon quits, therefor doesn't count as a Greil Merc until the next game (<_<; ). Elincia is a completely unique class on a character with oodles of plot (probably the 2nd most important character in the game beside Ike? At least for PCs anyway), Jill/Marcia/Nephenee/Mia are all widely used characters who, again, as a point in their favor, represent their classes well.
...yeah, my point about "unique, unrepresented class" was mostly that its a point in their favor, not the only reason to rank someone.
