Final Fantasy 10:
Tidus: 9/10. Hastega? Yeah, that's about it. Gets Haste early, breaks game, and then gets Hastega/Slowga/Quick Hit later on to break the game even more. Could use better durability, but speed hax in the FFX system is awesome enough as is.
Auron: 7/10. Durability. Just having the strength, HP and defence he does makes him useful, and the breaks add a good bit to that early on as well. Could do with some more variety and/or speed, but he's still a damn good character.
Rikku: 5/10. Fun niche with the items, but she's the most replaceable character by far. Items are, for the most part, tricks covered by other characters for the majority of the game, and without the cost. Healing items are usable by everyone, and I didn't find stealing was useful until post-game, really. Still has the speed and Mix to have a lot of use, just not as much as everyone else.
Wakka: 8/10. Gains 2 points here for Attack Reels alone, seriously, considering how easy it is to get Limits in FFX. Otherwise, good accuracy, strength and durability keep him as a useful party member, and the status helps in specific situations.
Lulu: 7/10. Since most enemies have weaknesses, she's pretty damn useful throughout for randoms, and has solid damage against most bosses. The speed and PDur really drag her down, since the evasion isn't all too noticeable until endgame.
Yuna: lol/10? Yeah, 10/10. You have to be pretty damn stupid not to use Yuna. (Hey, guess what? I didn't use Yuna until the Mega Graviton Sin fight... >.<)
Kimahri: 0.5/10. Has theoretical use? Everyone else is better at what they do, and with FFX's battle system, there is no reason to use Kimahri ever outside of his Limit Breaks and when Yuna's gone, and then you can just use items to fill Yuna's niche that he can cover.
Fire Emblem Armors and Lancers:
(Cutting FE6-7, since I haven't played them.)
Gilliam: 4/10. Ehh. Potential early on, but nothing special.
Amelia: 3/10. Yeah, she -can- be good. But she's underlevelled and way too late to actually be of any use.
Duessel: 6/10. Actually not too bad? The high levels help a lot here.
Gatrie(9): 8/10. Actually really damn useful. Tanks, has decent enough speed to at least not get doubled early on, and lategame, has the defence for weaker enemies to tink. Fails it up against most bosses, though.
Brom(9): 6/10. Starts off dealing way too little damage to do anything useful. Can become half-decent with some training, and still has decent-ish defences, but... ugh, that damage.
Nephenee(9): 8.5/10. Strength, speed and Wrath. Yeah, Nephenee's a beast if she can survive, but her durability's not the best. Might need some help early on, but definitely worth it.
Devdan: Not gonna vote on him. Never even wanted to use him.
Tauroneo(9): 5/10. Has speed and strength, just low defences for an armoured unit and comes way too late to make use of this, especially when there are better characters for what he excels in.
Aran: 7/10. Most of this comes from availability, because a half-decent character in the Dawn Brigade?! Yeah. Otherwise, a bit average, but definitely usable.
Meg: 5/10. Ugh. Nope, I'm sorry, I've never understood Meg hype. She's got poor defences on the whole and that's meant to be her forte. Screw you, Meg.
Tauroneo(10): 7/10. As with FE9, but much better availability. Still not great, but better, and his average stat spread looks much better when compared with the DB.
Nephenee(10): 7/10. Aran Mk. 2. Bit of a shame, since she was godly in FE9, but I've never really found her worth in FE10.
Brom(10): 7/10. Brom, on the other hand, improved a decent amount, making him at least above-average.
Danved: Again, never wanted to use him, so no rank from me.
Gatrie(10): 5/10. Oh, the nerf.
His defences seem so much worse now, and he's lost that speed advantage he had, which makes a world of difference. Much worse on availability now as well. ;_;