I've never played a resto shaman but my raiding toon is a holy priest so i'm totally biased but for me (I have played holy pally and resto druid) holy Priests are the most fun healer in the game.
They are also extremely efficient (even before the spirit buff) and the PMC set is amazing. They have very powerfull heals in general and master in aoe healing.
If I were you, I'd stick with the priest, probably easier to manage (1 key for direct heal, 1 key for aoe heal, and bind pom to every attack key you use) in a multiboxing context.