As a Holy Paladin, I'm used to working with the limited, albiet powerful, toolbox available. Yes, we have more "I just saved your life" buttons than any other healer, and our raw HPS is at the top of the healing charts. Tanking with a Paladin behind you means that you don't worry until you're sitting at 50% HP - where as a Druid healer will have you concerned (unless you see HoTs ticking). Sure, they can pull Swiftmend/Nourish/Living Seed out - but the Healadin is going to keep you bathed in Holy Light until you start to glow.
Even though our healing toolkit is technically limited to three (five if you count SS and BOL) spells, we have several CDs to help ourselves out. Mana conservation, 100% crit, damage reduction, and Aura Mastery - just to name the talented ones. These are a lot of situational cooldowns to manage, but you can start to tell the average Paladins from the great ones, just by looking at CD usage.
Now the Priest
Holy bouncing heals Batman! At 65 I've got more heals than I know what to do with, and I'm not even sure that I'm prioritizing them right. I've got my PW:S, Penance, Flash Heal, Renew, Binding Heal, Greater Heal, Holy Nova, and Circle of Healing. As a Disc Priest I obviously tend to lean towards PW:S and Pennance, though I've noticed that I use a lot of Renew and Flash Heal as well. Greater Heal is second only to Prayer of Healing for least cast spells - even Holy Nova ranks higher simply because it's an instant cast.
My typical instance involves me keeping shields on the tank (and the over eager DPS who pull agro), and using renew as a buffer between shields. Penance and Flash Heal fill in the rest. If there's a dire AoE heal need, I use Holy Nova if I think they'll die before PoH goes off. I'm not 100% sure, but I'm fairly certain that given the cost of the GCD, even putting a shield out to proc Borrowed Time isn't a smarter move. 1.5 sec GCD > 25% haste on a 3 second cast.
Once I pick up PoM that will go into my instant heal rotation. I need to read up on how it works though, as I'm not 100% up on the mechanics.
Back to the point
My point here, is that as a Disc Priest (Holy is just as bad I'm sure) I've got a veritable ton of heals to choose from. Fast vs. slow, AoE vs Single, HoT vs Direct. So many choices. I think this really adds to the power of the priest, but I can see why so many priests can't get a full grip on their class. As a Paladin, every target is a nail - you just choose which hammer to hit it with. With a full box of tools, I'm loving the choices. Finding the right heal for the job adds something to the class for sure.
Of course, for a new player this might be overwhelming. One of my office mates is trying out a new priest, and I'll see what she has to say about it later this week.