I've decided to list characters I find most usefull in the fire mblem games, as well as ones I don't like here, please be polite if you wanna respond, it works for me so I'm sorry if I "diss" your favorite unit, no sarcasm intended. I've mixed in some units from Sacred Stones as well so don't get confused. MOST USEFUL: -PoR 1.Oscar (my favorite unit, when I give him sol he is one of my best units, and his speed is wicked, first unit I change class, wich happens after Greil dies usually, and I always give him a seraph robe once he changes class) 2. Titania (one of the few starting paladins in the games I've played that's not worthless at the end) 3. Ike (I use wrath vantage and miracle against black knight instead of aether, he's strong enough without it and the occult can help other units in the endgame) 4. Sothe (I've been tight on gold and he saves me there, I don't like to fight using thief type units so Volke being able to change class doesn't impress me) 5. Soren (might be the best Mage in the game) 6.Tormod ( he might join late but he is really tough if you add bonus exp or use him to pick off weakened enemies) 7. Astrid (she levels up fast, and give her sol and Oscar as well, they can be a wicked combo) 8. tanith (I like using reinforce to draw naesala away if I forget reyson and sometimes to soften up enemies) 9. Giffca/tibarn/Naesala (you can't really beat these guys, and I personally use naesala more) 10. Nasir (well, you cant argue about anything other than his movement I believe) 11. Lethe (always works out for me more than Mordecai,and the instant transformation saves astrid in her recruiting, I always put her up front in that chapter and mover her behind Astrid) 12.Muarim (despite the penalty from the demiband he is a great backup unit) 13. Nephenee (I really don't know what her toughest point is,she's like an all rounder for me) -Sacred Stones 1. Franz (excellent starting stats and well balanced, and excellent for fighting the final boss, especially when he has an A support with Amelia. I tend to split the stat boosting items between the two, and I like to make him a paladin rather than a great knight.) 2. Amelia (this one will require some babying at the tower of Valni but is DEFINETLY worth it. As stated above she's great when paired with Franz, and I've beaten the boss using just the two of them in one turn. She can easily become the best paladin if you put in the effort) 3. Ephraim (the only one of the two main characters I don't need to baby, unlike Erika he's got a rather solid defense) 4.Natasha (she requires some patience, but as a bishop she's really useful especially if you've used up myrrh's dragon stone. Give her purge and she can take care of the Draco zombie guarding the gate on the next to last chapter, without you having to risk your units in a close encounter) 5.Vanessa (if you put in the work early her movement can make her extremely valuable in early chapters) 6. Ewan (I always make him a summoner, he is far better than Knoll) 7. Lute (easily probably one of the best anima users) LEAST USEFUL: -PoR 1. Mist (the combo of high magic and sword using kills it for me) 2. Reyson (I just don't find use for him except talking to Naesala with he has no attack to speak of and granting a unit another move is just not high on my list of importance) 3. Lucia (horrible defense and can't dodge real well compared to Stefan, Zihark, or Mia, she has died the most on me) 4.Volke ( a waste of gold, since he charges 50 gold per lock and not good at fighting either) -Sacred Stones 1.Seth (as the usual advanced starting unit this is more like a trap for people new to FE games, he seems good at first but later shows that he is terrible stat wise) 2. Marisa (I don't like myrmidons to begin with but she joins somewhat late for her level and I personally don't think it worth the effort, especially if you've been using Joshua) 3.Tethys takes a lot to level up and with the only ability being to grant an extra move, she's not a unit I'd bother with.)
NOTE: This is just from my play throughs on the main game, not the trial maps, and it's just for my style, I'm sure every unit can be useful, it depends on your style, I prefer to use more balanced power, and with good defense (knights are just too slow for me usually) instead of units with high dodge chance/strength but with low def./res. so yeah please comment guys and gals!