My entire roster consists of mostly of many Dark Knights, War Monks/Clerics, and Griffon Riders. I use Griffon Riders/Wyvern Lords for Support collections using Champions of Yore 2, and whenever someone can class into Dark Knights or War Monks/Clerics, I try to get those first since they pass useful HP replenish skills. Coming in a close second are Heroes for Sol and Tricksters for Lucky 7.
If they count as the same class, then War Cleric/Monk, at 8. If they don't, then it's a tie between Dread Fighter, Hero, and War Cleric, at 6. And if I'd answered this one day ago, it would've been War Cleric at 7.
Dread Fighters: Chrom (just trying to max Resistance; I'll use Spirit Dust for the Magic), Walhart (need to get to level 30 so I won't have to go through 10 levels of Wyvern Rider), Inigo, Laurent, Morgan, Alm (haven't used). Heroes: Flavia, Cordelia, Gregor, Nah, Gerome, Gaius. War Clerics: Lissa, Maribelle (just wanted to see it), Kjelle, Sumia, Cynthia, Cherche. MU before reclassing to Bride.
Official Bride and Wife of Noire (of the Fire Emblem Awakening message board)