WoW.coms Raid Rx guide:
Didn't see any Onyxia guides so I started this thread. I disagree with his suggestion to use Holy Nova, as it only heals the 5 people in your party, which may or may not be in range of the spell, plus its much harder to know if you pulled aggro. Personally, for the initial whelp phase I use mind sear, even though a shadow priest can do it so much more effectively than a disc. priest.
I kinda like his idea of sending a tank to intercept the sentinels at the entrance way. I personally don't think the main tank should do this, as he needs to be free to grab onyxia when she lands and not be tangled up with another add. However 2nd phase lasts so long, it does tend to help give the mt something to do.
Further, last night I was not consistently getting raid warnings about her deep breathes and was caught many times in it. If I'm at full health I can survive it usually. Also in second phase I would often run a different direction than the tank to get to the wall, which made getting back to the tank (who was also taking damage) very difficult. Fae also seems to be a lot more fragile than Ripsaw in terms of main tanking. (Maybe because he only has off-spec tank gear)?
Anyways during 2nd phase I think the healers with good aoe damage should break off and help get the whelps down (mind sear from priests works well). Three of the healers should be respectifully dedicated to healing the tanks and the other 3 healers that break off to aoe should break off aoe and heal raid when necessary. Those healers should be fully on raid when the bulk of the whelps are reduced.
NOTE: The ideas presented in this post are just my opinion and are by no means the official practice for the guild. A raid leader will implement the official methodology.