GAWD TIER: the 3 lords (Claude, Dmitri, Edelgard) and Lysithea
A tier: Byleth (fem Byleth is slightly better, she gets access to pegasus knight and darting blow) Leonie, Ingrid, Petra, Catherine, Hilda, Lindhart, Seteth, Felix
B tier: Sylvain, Ferdinand, Annette, Mercedes, blah blah blah
Honestly it really doesn't matter unless you're playing on maddening. On normal you could force everyone to be priests and still beat the game.