Originally Posted by
BillyMole
Your suggestion that the glyphed imp be tested against the glyphed felguard is silly. Glyph of Felguard is never appropriate for demonology, as it is only 5% and only on Legion Strike. Glyph of Incinerate will always be a larger DPS increase if you are using the Felguard.
That said, on anything with only one target, or a flying target, the Imp will win. However, your list of bosses on which to use the Felguard is incomplete. Basically any boss where there are two targets to hit, the Felguard wins, and especially any boss with add spawns. Additionally, certain fights will favor the Felguard anyway if there are either burst dps phases followed by nothing, or periodic vulnerability debuffs.
Felguard used : ODS (if your tanks stack them, which they should), Magmaw (adds), Maloriak (adds), Halfus Wyrmbreaker (adds), Twilight Council (burst phases, 2x stacked if your tanks go for that, this one is arguable), Cho'Gall (slimes, and if you're not sending in the Felguard to storm during the slimes I'm going to slap you), Conclave of Wind (ONLY if you are on the nature platform)
Imp used : Atramedes, Chimaeron, Nefarian, Valiona/Theralion, Conclave of Wind (if NOT on the nature platform), Al'Akir
Fully half the fights you should use the Felguard on (7 of 12 if you're on the nature platform for Conclave). On top of all of that, assuming you're not terrible with the Felstorm cooldown, the difference between Imp and Felguard is small enough that most people will not notice any difference should they choose to use the Felguard for all fights (other than bosses with a flying phase, obviously). The difference is there, certainly, but you shouldn't be losing sleep over it, and you should never, ever use the imp on any fight with adds that need to die.