prot.

as holy paladin you can pickup nearly every healer item that drops. you can wear cloth, leather, ....
nearly everything is good for a healer: crit, +heal, mp/5, int, .. doesn't matter except you're in raid-bossfights.

as prot paladin you can only wear plate, you need enough hitpoints so that a healer can react on the health
you've lost, you need enough defense to avoid crits, you need a good weapon with spelldmg (not that easy to find)
to built up aggro very fast, ..... it's very special gear.

my prot paladin had his healing gear complete long before he got his prot gear.