My guildmate warlock and I were running a small sample of testing today (5 minute tests per) and were getting similar results in the dps via pets.
From what we were finding first on the ptr was serviced imp was doing the most dps by a noticeable, consistant margin followed by fel imp then observer etc. We went demo and still found the dps ranking going to service imp>service fg>felimp.
Anyone have time to spare to run some dummys? I'm aware of how scaling and procs affect pet damage so took those in accordingly, yet still received the same results. I'm aware of the skada / recount bugs with letting pets attack alone and made sure to remain in combat for the duration. This is all on single target with wrath/felstorm on cd and most importantly - demon training glyph.