I've levelled my Paladin as Protection, switched from Ret at lvl25 and never looked back. You dont have to 'AoE grind' on certain mobs and avoid quests, you quest just the same as a Retadin does, but instead of grinding on the mobs one at a time and then drinking/bandaging you just charge in and aggro the whole messy pile, and then laugh as they die off your Reckoning and Holy Shield procs and your SoL heals you faster than they can hurt you.
Protection's weakness is big, slow, heavy-hitting mobs like Ogres and of course, casters. Killing these mobs first or avoiding them altogether speeds up Prot levelling immensely.
However, there is one large benefit to being Prot that nobody has mentioned; you can tank instances! You are almost guaranteed an instance spot, no more "Im ret btw..." and then groupkick. I got most of my levelling from instance runs, so I ended up completing all those high-XP dungeon quests, always had the best gear, and had a ton of fun playing with other people as a Paladin tank.
A Ret spec can level well, certainly better than Holy, and will please those among you looking for big numbers. To be honest though, the amount of extra instance runs you will get and the ability to survive multiple group pulls (4+4+3 is my record, with all cooldowns burned) more than makes up for it.
And there is the added bonus of snaring people in AV with Avenger's Shield, and watching Rogues die as they desperately try to damage you.
~sins