[kasnavada]

The best bet I've found for carrion factory is one of the indy shaman priest. It costs 110 gold (same as dryad), is sacred, gives the same research (by now you get what I mean) and has 10% chance of death magic. Just get some until you get death with one, and set the excess ones to research (that frees dryad for other tasks or more research).

The carrion lady is the best carrion generator / nature gem spent to summon them, but she doesn't have have access to 3 holy magic and can't lead too many undead. I rely on summon king to lead my undead carrion armies anyway (easy to get once you have the shaman I speak of above), since it cost so few death gem (which are not really useful anyway in early game and mid-game).

The last carrion summon is, however, a strong spellcaster and a good priest to boot. You can also use him to make a prophet and get 4 holy.