Let's get something cleared up right now: Efficiency is not part of my playing style. How well the unit can shave turns is a non-factor to me, while it's clearly important to you.
Let's get something else cleared up: The order that I listed the units in for their respective tiers only matters in the case of Boyd. Nowhere else.
Zihark and Nephenee made it to the top tier because Zihark's Strength usurps those of other Swordmasters, and he has Adept and the Earth affinity, and Nephenee's Skill ensures that she'll even always hit with ranged lances. Her Speed gives her a near unbeatable evade, and it does more than enough to compensate for her unimpressive Resistance.
Marcia would be higher, but even though she's got some solid evade, she's quite fragile. Higher skill Snipers will decimate her pretty quickly. If not for that, she'd be in the top tier.
Titania is only in the upper tier because she's just an experience hog in the beginning, and why you'd want to use her offensively in the early game is beyond me. She has better growths than most beginning-of-the-game prepromotes, but even though she can dodge fairly easily, her Defense is quite poor by Paladin standards. That, and she lacks Strength. (You know what? I stand corrected. Let's move her to Middle tier.)
We'll move Tormod one tier lower, too. The Est archetype (these are the ones who join quite late, but can become great if you put forth the effort into catching them up to the rest of your army) fits him perfectly, but he's inferior to other Ests because 1) other mages can use Fire, so his proficiencies aren't too special, and 2) raising either Soren or Ilyana is considerably easier, and warrants just as much (if not more) payoff.
Kieran would be top tier, if not for the fact that he's the least durable of the Paladins. He can't take hits like Oscar can, and he can't evade like Astrid can. (Though a support with Oscar can help him with the evade.) Basically, Boyd on a horse.
If I remember correctly, you told me that Elincia is superior to Mist as both a healer (because she can fly) and a combatant (because of Amiti). You have little time to get her to be able to use magic swords (though I pulled it off once), but she's still great if you invest all the bonus EXP you need to get her up to par with. Fits the Est archetype beautifully.
Ranulf is, statistically, the best of the game's beasts. He comes in late, but at the right level, and with fantastic starting stats. Only real weakness is his horrid Resistance, and that destroys his bid for the top tier.
Nasir is a fantastic combatant whose Speed allows him to double most enemies, and whose Strength allows him to kill in one battle just about every time he attacks, given that the enemy is not a General or another dragon. Sure he's got mobility issues, but on every playthrough, I used the Boots on him.
Largo, while having garbage defenses, has fearsome Skill and Speed for an axe user. His Speed grants him a solid evade, which doesn't do enough to COMPLETELY make up for his defenses, it makes up for some of it. Plus, he's got a 15% critical rate like every other Berserker.
My bad. About having Elincia twice. I meant to put Rolf there.
Makalov is better than people give him credit for (I get the feeling that people judge him by his character portrait...), but his Skill and Resistance hurt him consistently. Still pretty useful, though.
Astrid's only serious drawback is her Strength. She's got incredible evade, and fantastic Skill, but her Strength keeps her from killing all but the lower Defense units near the end of the game. Usefulness dies down in the last few chapters because of that.
Muarim is a hell of a lot more usable than Mordecai because of the miles of Speed advantage, but Muarim takes hits more often than he dodges. Combine that with his low Resistance, and he's but enemy Fire mage fodder. Still quite useful, though.
Lethe... bleh. Sure she can jump right into the action, but what people often fail to see is that near the end of the map, when the action almost always intensifies, she goes back to normal form and becomes quite useless. Nothing but evade, and lacks the Strength to put a dent in most enemies later-game. Basically, a Swordmaster without the 15% critical rate.
As for Tanith, Reinforce is overrated. The units that she calls for are just so frail, and can hardly take more than a couple of hits. Their only real use is ballista bait. Statistically inferior to Marcia.
I'll bump Calill down one tier. Between her use of knives and unimpressive growth rates, she's hardly usable for more than three chapters or so. Only real edge to other mages is her starting proficiency of B in all types of Anima magic.
Maybe Volke belongs in the upper tier. Thief capability is always a plus, and Lethaility, though hardly dependable, is awesome if it activates. Maxes Strength, Skill, and Speed pretty easily.
Rhys would be higher if he wasn't so **** SLOW. That, and his pathetic Strength keeps him from double attacking with the heavier Light tomes.
Mordecai... is only useful for a few chapters. His crap Speed really puts a dent in him.
Geoffrey can never be expected to reach any stat caps, and it is for that sole reason that he is in the lower tier.
Contrary to popular belief, Ena isn't unusable. Granted, you'll have to use Boots on her, but really, she's not GARBAGE. It's just that Nasir is superior in every way.
Ulki probably should be bumped down a tier. His nasty Speed hurts him considerably, though Vigilance adds to his evade.
Janaff is pathetic. Though having great Speed, he's mediocre everywhere else. Insight is completely unnecessary. While Insight makes him ideal for Gamble, but critical hits still have a pretty slim chance of happening.
Devdan IS unusable. His growths are inferior to Nephenee's. His starting stats are OK for his level, but he does not hold a candle to Nephenee. Lower Strength, lower Speed, lower Skill... lower everything. Honestly, you're best off forgetting him.
Brom sucks. All of his growths are inferior to Gatrie's, and his starting stats are hardly Knightly. A half-baked attempt at sacrificing every other stat for a slightly higher starting Speed.
Sothe scraps the bottom because HE CANNOT PROMOTE. Even if you kept Blossom, his stats are inferior to the rest of your army later in the game. Because of Blossom, he gains EXP slower than laguz. I feel sorry for the poor dupe who poured boundless amounts of BEXP on him, only to find out that he couldn't promote.
...That took forever. D: