1 week ago (Beta)
I like mage for the easy leveling and free portals and food/drinks and it is good class in pve and pvp.
I like priest especially for healing in dungeons and raids and battlegrounds/world pvp.
And therein lies your real conundrum. Easy levelling and independence, or group dependant and invaluable team-asset? Tough choice.
Personally I've done the priest thing (literally) in vanilla, so this time I'm going for a strong-independent-female warlock ;p
I pondered for a long time between Alliance or Horde (I vanilla'd as Horde) for the exact same reasons you are considering now, but Alliance is only composed of Elves and Humans in sizes large, medium and small, so I find them extremely boring to play (I tried...) so it made my choice easier to go Horde again.
Only you can make that choice depending on your experiences :D
And they say Blizzard games don't have bugs. - Anub'arak