1. MaxWell Max is based on how you use him. And how you raise his stats/skills/force arts. Honestly he'll need the proper backup depending on how you use him.
2. MerylBefore Class Change: 6.5/10 She's not bad generally a mage with versatile spells. She lacks Ice Spells however. Her main spells are fire based. Luckily the game doesn't have too many enemies that are completely immune to Fire. At higher levels she's much better by gaining lots of AoE spells. She even supports by using a Charm of Flesh when you're petrified. Considering for most of the game she's virtually the only mage you have you're stuck with her for magic purposes.
After Class Change: 9/10 She becomes entirely useful gaining a darkness and a light element spell. Added with improved Wind/Lightning and Fire spells. She's a beast and can handle most enemies alone. Even better for 1 on 1 purposes she's awesome with fire spell spam.
3. GaiaHe's the awesome character that dies in the storyline...so....yeah. Nuff said. Unless you hack him into your party....I have nothing to rate on him.
4. GrahamBefore Class Change: 5/10 He's a tank. Not much of one but a tank. Mainly he won't be pushed around so easily by any enemy due to resist knockback.
After Class Change: 7/10 The tank gain a few new moves. Mainly ones for mowing down small fry. However put him against big guy and Graham is goner.
5. ChiquititaBefore Class Change: 7/10 She's you're white mage. Expect White Mage stuff. Holy spells and cure spells.
After Class Change: 7/10 She stays the same pretty much just improved versions of the same moves.
6. BaronBefore Class Change: 8/10 Very useful for getting around the enemy unoticed and inflicting a lot of damage. Problem is he's no good on big mobs. If he's fighting a big guy he can be useful. Only main problem is put him against a Fire Dragon or anyone with fire moves and Baron is down for the count in 5 seconds.
After Class Change: 7/10 Although increased stats help him as well as complete resistances to Ice Moves. The new moves he gains don't help him out. He'll tend to use his ice elemental moves more than his normal ones. And he's no magician.
7. RhinosBefore Class Change 7/10: HP Tank. He obviously will have the most HP out of any character. Also being one of the strongest characters of the game physically. Mainly great for keeping the attention of the enemy you can sneak around and take em out. Considering he's rather slow at attacking.
After Class Change: 6/10 Although gaining a ton more HP and strength. He gains the same problems as Baron. He's no Ice Mage. And he likes doing big long charge up moves.
8. MarielBefore Class Change 6/10: Although a weaker version of Graham she has a healing spell. Making her far more useful by default.
After Class Change 7/10: Gaining Holy spells, better magic resistance, and immune to stunning. She stays pretty solid.
9. DryuBefore Class Change 5/10: The little cute dragon is just cute at this point.. At higher levels she gains a fireball and is actually smart to stay at a range instead of getting in the enemies's face. She also flies....(yay)
After Class Change 10/10: OMG Practically the must have character of the game. She gains moves of Fire, Ice, and Lightning. Also gains immunity to those 3 elements as well as a good amount of HP. If you can't decide who to take with you Dryu is the way to go.
10. FreyjaBefore Class Change 6/10: Meh she's a fire user and the only other true mage of the game. Not as useful as Meryl but she is immune to fire. However put her against any enemy that has a knockdown move or really if she's ganged up on she's done.
After Class Change 7/10: She kinda got the short end of the class change stick here. Becoming immune to knockdown is nice. However anytime she's ganged up on she's dead. She also doesn't like using her spells all too often.
11. KleinBefore Class Change 7/10: He's good at ranged attacks. But like his significant other. If he gets ganged up on he's a goner. But his use of Petrify arrows and Slow Arrows are very useful.
After Class Change 8/10: Immune to Critical Hits and Knockdowns make him slightly better. I don't see a reason not to take him other than unable to handle being ganged up on.
12. AdamBefore Class Change: 2/10: USELESS SCRAP OF METAL!!! Seriously he only has one attack and its no good. If you want a distraction I guess you can use him but he'll die in seconds even if he has great HP and defense. Just utterly useless.
After Class Change: 9/10 A much better improvement. Well worth the work you put into to getting his class change. Gaining the Holy Spell Gaia Nova and is able to fire it in rapid succession. Even gaining a Petrify attack. The only problem he really has is being maybe too aggressive.