Many guides suggest that for Demonology the Felguard/Wrathguard is the superior choice for DPS. So I sat down at a training dummy today and let each pet beat upon said dummy for 10 minutes.
Fel Imp: 18,179 DPS.
Wrathguard: 11.407 DPS.
Observer: 9,439 DPS.
Void Lord: 9.240 DPS.
Shivarra: 9,187 DPS.
I then sent the Wrathguard over to the triple dummies with Mortal Cleave auto-cast, and used Wrathstorm at every opportunity: 12,312 DPS.
Suspecting that the Wrathguard probably generates additional wrath, I took a stopwatch to count how long each pet took me to go from baseline to maximum.
Fel Imp: 425 seconds. (no need to move at all)
Wrathguard: 428 seconds.
Observer: 427 seconds.
Void Lord 428 seconds.
Shivarra: 426 seconds.
So I sent the Wrathguard back to the triple dummies, because it probably generates more wrath from hitting multiple targets: 427 seconds.
The minor variables are probably human error. Thoughts?