Up through the end of BC my only healing experience was on my Druid, which included raid healing through BT and MT Hyjal, and of course the obligatory 5-man healing. At the time I couldn't envision healing on any other class because I truly loved the total mobility that the Druid class gave me as a healer. Rejuv and Lifeblooms rolling on the tank and judicious use of Rejuv and Lifeblooms on everyone else can do marvelous things. And all done on the move. If you ever needed to do big chunks of healing you always had the option to blow swiftmend, or in the worst cases Natures Grace and then instant Healing Touch. Those of course have cool downs, so if you needed to do additional healing you would of course have to stand still a few seconds to get off Regrowth.
Then WotLK launched and everything was turned on its ear. I of course switched "mains" after playing my Druid as my main for four years, and Blizzard retooled most spells and abilities, including many of the healing classes mechanics. Mid-way through last year I decided I wanted to have a healing option again, but instead of just leveling my Druid I asked a friend what he thought I should do and he recommended the Paladin. I leveled that to 80 and found out I wasn't all that taken with Paladin healing and parked him for a while before coming back to him. I say "not taken" with it, but what I was really suffering from was "differentitus". Paladins, like every other healing class except the Druid, are a stationary healer. Outside of one instant cast healing spell Paladins have to remain stationary to cast their spells and that really bothered me. Particularly in PVP which was what was driving my desire to heal again in the first place. It had been my observation that if you stand still in PVP you were usually dead.
However I'm very glad I decided to give the Paladin another look a couple months later. Since then I've officially switched to my Paladin as my main, and I raid and pvp heal on him regularly. Once you get over the mobility issue the other advantages of the Paladin healer become very striking. The first thing I noted was the extreme mana efficiency of the class. Particularly if the player uses Flash of Light as their primary healing ability. Spamming FoL, with it's short cast time enables the player to heal multiple characters in quick order and Beacon of Light, which heals whoever its is placed on for the same amount of the heal, essentially doubles HPS. Of course it can double your over healing too. On those occasions where you actually need to regen mana, divine plea with it's one minute cooldown, is almost always up. Divine Plea regenerates 25% of your mana, but reduces your healing by 50%. Sounds horrible, but it's really not because it can be used in conjunction with Avenging Wrath which increases healing effect by 20% and Divine Illumination which reduces the cost of healing spells by 50%. You don't absolutely need to use the three in conjunction with one another, however you will see a great amount of regen if you do. Even while continuing to heal at a reduced rate because of Divine Plea. I've die, been battle-rezzed and been able to buff myself and get right back into healing through these abilities, ending the fight with close to 50% mana. In addition Paladins gain back mana through critting, so critical rating is of utmost importance, followed closely by haste.
A typical 5-man healing endeavor would entail me putting a beacon and Sacred Shield on the tank and hitting him with Holy Shock as required. I don't typically have to use anything other than FoL for healing, and if I have to heal any other group member because of random damage the Beacon on the tank takes care of him while I take care of the rest of the group. Unlike other healing classes the Paladin doesn't have a true area heal ability, so in those fights where a lot of group damage is present your only means of handling that is by spamming FoL in a rolling fashion from one member to another. It shouldn't take more than 4-5 seconds to heal everyone in succession, excluding the tank of course.
For those occasions where you find you have to heal someone for a great deal or they will die, there are a couple of ways of handling it. If it's the tank you have your big heal Holy Light, and depending on your gear can heal for 14-15k or higher. You also have Lay on Hands, which is your real emergency button and should only be used in true emergencies as it has a fairly lengthy cool down. For those group members that are in trouble you have Hand of Protection that will protect them from melee damage, and you can always blow Lay on Hands if you think you won't need it for the tank any time soon.
Just as important as a classes healing ability is it's tools for self-preservation. And no other class has better self-preservation than the Holy Paladin. When faced with a situation where survivability is questionable a Paladin always has the option to place their beacon on themselves, which of course continuously heals them as they go about continuing to heal others. That alone will save the Paladin more often than not, but in those cases where massive damage is being taken there simply is not better emergency button than Divine Shield, which absorbs all damage for 12 seconds. 12 seconds of complete freedom to heal in total safety while others regain threat.
Lately though I have been wanting to heal on my Druid again. Honestly I've had the desire to do just about everything you can do with my two hybrid characters, and through two mods I've been doing just that. Of course I have a full healing and Ret set on my Paladin, but I've also got a nearly complete 245 ilevel tanking set too. On my Druid I took him back up over the Summer leveling as Feral where I DPS'd and Tanked, but have since respecced and raid as Balance. A week ago I dropped my remaining Feral spec and switched to Resto, and have been having fun healing Heroics and in PVP with him again.
As I mentioned at the outset the biggest difference in my view is the mobility, but the primary Druid healing style is also completely different. Unlike Paladins, who have fast direct, and big bomb heals, the Druid class is mostly about healing over time. For someone coming from a direct healing class like a priest or Shaman that might take some getting used to, but really only until you realize the freedom that gives you. Direct healing classes are often very reactive, meaning you often won't start healing until someone gains agro, or has already take damage. But as a Druid healer you most likely already have HOTs running on a tank, so he is already being healed as he takes damage. As a Paladin, if I find myself in a situation where my group (or raid) is taking area damage I have to heal them one at a time, although in quick succession. But as a Druid I have something in addition to my primary HOTS that my Paladin does not -- a true AOE heal. I can easily put Rejuv on everyone in the party and just use Wild Growth every six seconds to keep AOE healing up. With HOTs rolling on the party I don't have to be a reactionary healer, but instead transform in a proactive healer, anticipating damage and dealing with it before it happens.
As I get back into the swing of things with my Resto spec, the only thing that I think I still need to rest is my mana efficiency. Whereas I had been quite spoiled with the mobility of the Resto Druid, I've become quite spoiled with the mana efficiency of the Holy Paladin. As I've only done Heroic healing as Resto, I need to see first hand what my mana efficiency is like in a raiding environment and I should see that Saturday night in ICC-10. More to come on this subject.