My argument for holy paladin is this. It's a very robust class - almost impossible to nuke down quickly.
Healers are always primary targets in battlegrounds. The key is to be able to take the burst, and this is what holy paladin excels at. Not only can it take the burst, it can heal, whilst taking the burst. Add in bubble, loh, hof and it's great for support too.
Don't worry about mp5. The base stats you get off the blues + epics, coupled with your BOW - and as long as your efficient, you will actually struggle to go OOM. I'm not quite sure on the figures, but i've heard many times, of holy paladins burst healing, whilst keeping there mana, overall, stable.
A guild member of mine is gunning for 3500hp, 2500 mana, 2800AC and about 150sp. He's nearing these figures, and it's working really well. The downsides are that, you are easily interruptable, and can't heal on the move. The nice thing about a stamina stacked pally is that the opposing side have to use up so much resources to take one down - leaving your dps to clear up.
I wouldn't necessarly say better than a priest, certainly more durable however. Resto Shaman is another option. Again, unless you are a rogue and can stunlock from 100% hp to 0, you won't take one down solo. Within 3 minutes anyhow.