My personal choice is feral for pve and balance for pvp, but i'm sure plenty of people have good things to say about one or the other in any given situation.
Except for cat dash and bear feral charge, you don't have a lot of ways to close distance unless you start in caster and root then run at the other player ;)
With balance you have more ranged options, as well as potent healing as it's boosted by your damage gear and you have a bigger mana pool. As I said though thats a personal preference as I enjoy being the battle-medic in pvp, thowing heals and wrath around equally ;)
Plus if memory serves there is quite a lot of good caster stuff in the first few quests in HFP, although the same could be said for feral.
Feral is also good, especially for stealth defence on nodes with bear as the "oh sh*t" button to help you last until help comes ^^
If the priest is going to be a medic though, you may want to consider feral for the tanking/dps options. Especially if you plan on lots of AV. Good tank/healer combos are great when taking down the commander.
Edited, Dec 11th 2007 8:41am by kadanis