I like hobgoblins or undead better for large-scale plotlines than say orcs or kobolds. They'll be ok for a sidequest here or there, but if I were to have the bad guys be of one race, I'd have something intelligent or at least have the ability to plan ahead. Undead (or at least the liches/clerics that use them), Hobgoblins, Evil Humans and Devils are all good options for that goal and selecting one depends on my mood or inspiration. Kobolds, Ogres and Orcs are simply too small/dumb to make long-term villains.
Cheers,
Illirion.