[PvK]

None of the types are better in all ways. For plain melee, armed longdead tend to be better fighters than ghouls. But ghouls have minds, so they absorb attacks like Mind Burn, Soul Slay, Ithilid Mind Blasts, etc., which makes them very useful against those dangerous threats, when they exist.

And for another example, even unarmed soulless are better at soaking up some kinds of attacks than longdead are. It's more a question of how it makes sense to organize and use them all in what circumstances, than which is the best. Best is making the best use of all of them in each situation.