There have been polls and threads on this in the past. Clannfears usually win.
I also vote for Clannfear if I had to just vote for one. Because they are very aggressive and fast.
... And which do you prefer out of daedroth, xivilai, and storm atronaches? Feel free to go onto detail!!
It really depends on the situation. If I had to pick just one of those, probably the Storm Atronach. Lots of health and reasonable attack.
But against Liches or other spell casters I might pick a Xivilai because it has spell absorption. Except of course against Goblin Shaman who use shock, the a Storm Atronach because it is immune to the shock attacks.
Clannfears are great against enemies that run away, like necromancers and conjurers. Because they are fast enough to catch them.
A Wraith is great against warlords and other enemies with a "normal" weapon (ie not enchanted, Daedric or Silver). It's fun to watch a warlord try to damage a Wraith with a big Ebony Warhammer and not have any effect.
Storm Atronachs and Daedroths make great distractions. They are not very fast, but they can absorb a bunch of damage. Storm Atronachs are a bit more powerful, but at the cost of more magicka.
Liches are great. They don't attack fast, but when they do their attacks can be powerful. they are also hard for your enemies to kill.