Wizzy? You want to hit them with Manticore damage (and have lightning resist)
DH? When you catch them between smoke or when they are OOD? You want to hit them with a Manticore.
Get a WD after SW is over? Manticore.
Monk when Serentiy is down and you get that one or two hits in that are not DODGED? Manticore **or** Windforce
Barb? Well, the traditional run after you Baba can be beat with a Buriza. Jump-Rend barb you just need to time Smoke correctly and then hit them with Manticore damage. The throw Barb is just a bad DH -- higher EHP, lower DPS and no DI.
Under no circumstances will a Calamity ever be the best for PvP. Watch the prices tumble.
Calam's are fun for low level farming or Ubers if you have high stun/freeze, but they are the worst choice for PvP.