[Taryble]

Already having a healer/dps caster (Holy/Shadow priest), I recently levelled a Paladin.

Here's the breakdown. None of the specs play like a caster - even Holy only has 1 "attack" spell. Most of the time, you're beating on things with your weapon of choice. Seal of Light + Judgement of Light for soloing elites, Seal of Retribution (or Command if you're Ret spec) until you get Seal of the Martyr. Judgement of Light always, unless they're not hurting you and you're low on mana, then Judge Wisdom.

Holy - most mana efficient healer in the game. Also the most HP and most health of any caster. Slow levelling, but you won't die as long as you have mana. Which you'll always have.

Protection - Die? HAH! AoE grind like never before! Seriously. Unkillable unless you're crazy.

Retribution - Slightly more squishy than the other two. Levels fast. 2-3 targets at a time. Is capable of stupid DPS. Can solo 90% of group quests until you hit Northrend. Believes that killing things is an acceptable substitute for eating and drinking for hp/mana recovery.

I levelled Ret to 78, when 3.1 hit and I went Prot. I levelled EXTREMELY fast (faster than either my hunter or my priest, who levelled shadow). So far, I've only died 20 times on my paladin - and 3 of those were while Prot tanking regular 5-mans, 4 were on unlucky pulls while raiding as Ret. 13 deaths from level 1-80. Pretty freakin' solid.