Paly can do anything pre-lvl 50. I leveled to the 40s with Ret. From 40 to 53 I've been Prot. As a Ret, I was able to tank and heal instances. I only noticed a lack of healing when I entered BRD. So... My guess is that pre-BRD, you can fill any role without spec'ing for it.
That said. Ret is considered the fastest leveling spec. I'd suggest 10 points in holy, the rest in either Prot or Ret. The 10 points should get you +INT and lessen spell knock-back. Both will keep you alive longer.
As you have healing and judgements/seals to generate health, Mana is more important to keeping you alive. Make sure to take the +Int and not the +Str...
If you spec Ret. Get a good 2 hander. If you go Prot. (Which is a lot of fun) Just make sure you get a 1h wep, a shield AND a shield spike. Google "Paladin, AOE" and learn to do it. It's fun and pretty easy (Compared to doing it with my mage).
I personally suggest you go Ret until you hit the 40s. It's fast and easy. Then respec to get Prot & AOE.
My questing has been plently fast, you still have the ability to burn down mobs, and I've been able to solo several elites that were 3+ levels better than me. My best yet was a lvl 63 Huntard jumped me at Marshall's Point. I lost, but it took him 5+ minutes for him to kill me. that's 10 levels above me.... (yeah, i know a huntard)