This is pretty fun, actually.
Eliwood - 7/10. He has great availability, and a fantastic support game. He's pretty well-rounded, and gains a mount upon promotion. Unfortunately, his Strength is pretty disappointing, especially when combined with his Sword lock, and he's stuck at level 20 for a while.
Marcus - 5.5/10. He has his godly earlygame (helpful, since earlygame is where it's hardest) and availability going for him, but he'll be outclassed by the time you start promoting.
Lowen - 9/10. If memory serves, he has the best durability of the cavs, and in a game where everyone one-rounds later on, that's what matters. Add his good supports, availability, and base performance, and you have... Lowen, a very good character. Plus, he's yellow. Omg.
Rebecca - 3/10. Lolarcher, though she is pretty good for her class. Not that that counts for anything, but yeah.
Hector - 8/10. He's very tanky, which is nice. His supports aren't bad, and he has axes... Unfortunately, he's also somewhat slow and has low Hit, and he caps at level 20 for a while.
Oswin - 8.5/10. A beautiful tank, he has amazing supports and earlygame, and his lategame isn't bad. Minus points for actually failing to double quite a bit.
Guy - 8/10. Despite lackluster Strength and Sword lock, he has his supports (he can support with Matthew for full Atk and Crit. And Acc, little though that's worth - he can do the same with Priscilla, but she has a lot of good options, so that's tough for him to get), and he has a bit of Defense to back up his Avoid. Then his attractive crit boost upon promotion, and the fact that he has the earliest promo item (Raven wants it, yes, but he also comes at level 10 in the same chapter as it, while Guy should have passed that by now), and he's a pretty good unit. That was long, too. And this is only making it longer. Hm.
Merlinus - 10/10. Godly Con base, 100 HP growth rate, and he gets +4 Movement upon promotion! The perfect unit!
Priscilla - 10/10. Very mobile healer, thanks to her horse, and ORKOs even many bosses upon promotion, while still having good Avoid, Movement, and staff utility. Her affinity may fail, but she has a support list completely packed with amazing units, like Raven and Oswin.
Raven - 10/10. Good base stats, great class, has access to the earliest promo item (if Guy doesn't take it), and he has fantastic offense, able to cut down bosses like they're not even there. WTC, high Avoid, and decent Defense gives him a great defensive game, too.
Canas - 4/10. Fragile, and has a weak start. His power doesn't do much when everyone one-rounds non-bosses, and his boss-killing ability doesn't offset his bad durability and earlygame. He does have a monocle, though.
Dart - 3/10. Has a terrible start, is very expensive to promote, and his h4x offense doesn't make up for his lackluster defense, much like the Canas I just rated.
Fiora - 6/10. Flier utility, and she has a nice support game - she can triangle with Sain and Kent (who have similar movement), getting a match for her affinity, and an Anima (for that much-needed durability), or she can go with Kent and Eliwood for more Anima (though Eliwood will lag behind until he promotes). She's pretty underleveled, but she's rather handy in her joining chapter and quite a few afterward. Unfortunately, as a Pegasus Knight, her durability is bad and will always be bad.
Legault - 7/10. About as combat-ready as Thieves go, but he's still pretty fragile. Stealing is still a nifty tool, though.
Ninian - 10/10. Same as Nils, only this time, she can massively buff your stats - even coming with the (downright amazing) Ninis' Grace.
... Okay, I'm too lazy to finish it. :P
Yeah, right now, the high numbers aren't balanced with the lower numbers, but then, most of the failures start coming in later.