Bears are pretty special. They’re so different than the shield tanks that it’s hard to understand just how special. Here’s my list of things other people should know about bears so that they will know how to use them well or help their raid’s bears improve. This list gets more and more detailed and complicated the further you read, so if you feel like you understand “enough”, you don’t need to read the whole thing.
I’ve personally melee dps’d and tanked Onyxia (phase 1) and Nefarian (phase 3) in this fight. Heroic Nefarian is more difficult than Heroic Valiona and Theralion, but easier than Heroic Cho’gall. We used 3 tanks for this fight.