I use devastators in my Blood Angels, generally more for anti infantry or light vehicles killing. More a defensive unit to me really as I take 2 missile launchers and 2 plasma cannons.
Make a good deterrance or effective killer of troops silly enough to make themselves a target.

I still will take a predator as well though for the lascannons and autocannon. I dont bother with the heavy bolters on it anymore.. always seemed to do naff all!