I'll put what I said on his Facebook post:
Plenty to choose from, for me personally it would only be TNG, but each series has some excellent choices.
TNG - Hugh, Gowron, Moriarty, Guinan, Lore, Tomalak, Sarek
DS9 - Martok, Garak, Weyoun, Dukat, Jem'Hadar.
VOY - Hirogen, Seska, One, Annorax...