I've played the game twice now, and the only character I haven't used yet is the Minister.
I think I more or less had my Dream Team this time around:
Archer (of the Clouds) ... her class wasn't crucial, I hardly ever used her spells, but her pre-emptive shots are awesome and essential.
Magneto Witch ... I always like to have one character with paralyzing spells, so I didn't regret choosing Magneto for her. In my first playthrough I had a Thunder Monk, but she has some Earth spells too, so I think she's better for that.
War Monk ... powerful and strong with very useful skills.
Commander ... very strong, very resistant. Combined with the War Monk - unbeatable!
I had the Archer as my leader, which turned out to be the best choice, too. She was a great asset all through the game, but she would only have sucked in the final fight.
The three that I had were an awesome team together. The Witch boosted and healed the party (I had plenty of the Mercury thingies from the Ghouls, so she didn't need to have a healing spell), the Monk has some great never failing spells that debuff the enemy, plus he has a death spell that kills off the spiders quickly. And since he was also the one who attacked the hardest, I just had the Commander cast his Dictator spell on him all the time, so beside his own action, he would also hit the boss twice.
With this party I beat the final fight in the first try.
I don't think I'd trade any of those characters next time around.
The Rogue is a good fighter too, but I wouldn't trade her for the Monk or Commander, and certainly not for the Archer. Which leaves only the Witch, but in the final fight her boosting spells are crucial.
So yes, Archer - Magneto Witch - War Monk and Commander are my dream team!