My favorite unique class is Holy Swordsman (T.G. Cid is the coolest character in the game IMHO), combining the nifty sword techniques of Agrias, Meliadoul, and Gafgarion!

My favorite combination of generic classes is Knight/Calculator. I'm not a big fan of the knight's abilities, but it allows them to equip the best swords (Excalibur for the guys and Ragnarok for the gals). The Calculator abilities are great once the party is maxed out in levels. Then I can always miss my party by calculating against levels other than ones divisible by 3.