Ap or Altap

If there's luck, it might still work. They're good for mowing down neutrals.

It's much easier to lure and defeat mobs.

I'm just starting to learn about demons, but I really like the jump attack of the stronger ones; it's not even so much the jump itself, but the damage.

Well, with imps, it's pretty straightforward: first, upgrade for pets against mobs, then upgrade for the hero and frenzy.
Fire hounds are great :) I haven't figured out the horses yet, but the nightmare ability seems more appealing in theory. The draining aura is also not bad, but for it, the horses need to live a long time, and it's not very effective against mobs either - I'll only keep a stack of horses under constant attack in strictly defined conditions.
It's roughly the same with cave lurkers as with imps.
And with devils, I don't know... probably upgrade for attack, it's a little tougher too.