I can't help with your exact question because I can only speak to level 80 specs, but the general principles should apply and maybe some of this will be useful. The interesting thing about PVP healing with this class is that there are a few specs to try rather than there being just the one clear path. Each has advantages and disadvantages and how useful each will be depends on what you're doing (battlegrounds? world PVP?) as well as playstyle. But here's my 2 cents. I'm sure others (hai Mike!) will chime in with their experience as well.
1. Deep Holy 51/20/0. This is still the bread and butter healing spec, and most of the top rated paladin healers are using it. There is some leeway here and there on a few points, but a typical 80 spec looks
something like this.
Advantages: Great healing power. More range on judgements. Strong defensive spec with good survivability. Beacon is very handy for keeping yourself healed while focusing on others.
Disadvantages: OOM. A lot.
2. Holy/Ret hybrid 32/0/39. A typical 80 spec looks
something like this. I don't see a lot of people using this much anymore, presumably because the power is not really there.
Advantages: Excellent for mana longevity. An extra CC with Repentence. Improved movement speed, lots of crit, and Divine Purpose.
Disadvantages: the healing power is lacking. Keeping squishies alive can be difficult.
3. Deep Prot 19/52/0. Yes,
it's a healing spec!
Advantages: Stack Stamina and your spellpower is also through the roof. 10k Flash of Light crits. Hammer of Justice every 20 seconds and an extra silence make this a great spec for control and survivability. Endless Divine Plea=endless mana. You're outrageously hard to kill.
Disadvantages: No. Instant. Heals. You've got a few tools to avoid interruption, but people who know what they're doing can neutralize you pretty easily. Try to use this spec for PVE and Bodhi will personally hunt you down and beat you with a dead gnome. Lots of people will whisper you with insults because you're a prot pally in healing gear and they think you're an idiot or else bought your account.
Edit: edited out the stuff about AD because my info was outdated.
Edit again: bad link.
Edited, Jul 22nd 2009 3:56pm by teacake