I can talk a bit about the druids in a team.

I run 5x druids. I originally choose this as I was a bit uncertain about which group composition I should pickup. And people generally said druids was okey for Instances. And they are. Im not in heroics or anything, just focussing on leveling atm.

Im a casual player and plays maybe 2 times a week, so its also easier for me to only have one class to manage and to read up on when changes arrive.

If you include a boomkin in your group you would need to manage the Eclipse Proc to maximize the dps on this toon. I don't know if the extra management is worth the efford of the buff.....

I have enjoyed playing with the druid team so far and I hope they will be good enough for the end game stuff when I reach it at some point in the far future lol