Deviling is suicide. When a monster goes berserk, he takes on an element. Also, WS have a skill that is elemental and generally does 14k+, with Devi, you have no chance of survival.
As far as shields - I personally prefer Toad. 4/6 monsters are Demis, and the only skill that can really hurt you hard is Soul breaker by the Assassin Cross, followed by a Sonic Blow or Meteor Strike; but even then, you can still survive if you hit em just in time.