The Holy Paladin is an exceptional single target healer.
However, they are seriously lacking in party or AoE type heals.

In encounters where the damage is focused on one toon, they'd be great.
But if everyone is taking damage, which is often the case, they have issues.

A shaman (chain heal), druid (wild growth) or priest (holy nova, prayer of healing) have a much easier time as the healer when boxing. I'm not saying the pally will not work, but the priest is much easier.