If you plan on trying to solo level, strong retribution focus with a two-handed weapon is a good option. Something like this:
http://db.vanillagaming.org/?talent#sxZZyf0t0fVo.
Above 20, AoE leveling becomes an option if you want to stay spec'd as Prot for instances. There's already a thread on here about that.
http://forum.nostalrius.org/viewtopic.php?f=43&t=14088Holy leveling is an option, but not a very strong one. It can make sense to put 11 points into it to get consecration (and Divine Strength ain't bad either), but Holy just isn't equipped to be a damage spec. It's really just meant to be taken as a second spec for Prot just as it is with Disc for priests when leveling.