Personally I think that Druid's have drastically changed compared to Wrath or even TBC, while raiding I noticed that I take the responsibility as a tank healer (while in Wrath I hated it). We don't have the tools Paladins have but with our HoT's I believe we still have an advantage in heavy movement fights. But then again Disc isn't so bad either with those "all absorbing bubbles of win!" I haven't played on my Shaman yet but they probably have something awesome as well that Druid's could use... Let's compare, let the battle begin!
Raid healing: Priest 1, Druid 0
Tank healing: draw
If you ask me Priests are godly for raid healing (yes Potz!). If you're looking for an alt to level and to heal raids in the (near) future go level a Noam Priest! The nice change to Efflorescence in 4.1 and Tranquility will even the battle between Priests/Druid but as long as Druids don't have a short cooldown burst heal, we're not going to win this one. However there is one part where we might own Priests and that would be mana. Moonglow, Furor, Revitalize, Innervate and OoC (LB in ToL) are giving me so much return that I am already considering to just drop +Spirit gear and just get more regen as I get more +Int. Priests have a decent set of tools to preserve/regain mana however they spend it like it's HoT.
Raid healing: Paladin 0, Druid 1
Tank healing: Paladin 1, Druid 0
Paladins are still king of the hill when it comes to tank healing, not only because of their healing output but also because they have nice cooldowns they can use to save people. When it comes to raidhealing they lack the constant ability to heal several people. Paladins have nice AE heals, but they're all on cd.. Plus you can say what you want, but that odd winged knight does not own my Tranquility... While Tree of Life is just a Druid version of their wings, it also alters our Lifebloom (which is again beneficial to raid healing). Sorry Thor, you lose!
No. Idea. As I've said I haven't played on my Shaman yet and our guild doesn't really have a Restoration one present. From what I know about Shamans I would say this:
Raid healing: draw
Tank healing: Shaman 1, Druid 0
Earth Shield and Riptide's haste buff make Shamans heal hard and fast on one focussed target but raid healing wise I would take the bet and roll Druid!
As you can see, we're not the best around. But I still heal like a nutter! If you want to be the best of the best in a roll then you might want to skip Druid but if you want to have an awesome class, don't look any further!