Also maybe it would be good to have options later on to go DPS or something. :)
With that in mind, do you have a preference on being melee or ranged DPS?
Monk: Melee DPS
Paladin: Melee DPS
Priest: Ranged DPS
Druid: Melee or Ranged DPS
Shaman: Melee or Ranged DPS
The bonus to going with a Ranged DPS version is that, at least while leveling, you can do a lot of gear sharing between the DPS spec and Healing spec. I did my leveling as Boomkin, healing 5-mans as I went. Worked out nicely, as until I dinged 90, the only gear I ever swapped was trinkets.
Some more detail on that:
Ranged DPS specs:
Shadow (Priest): DoTs and channels. Short cast times, short cooldowns, and procs. Fast-paced, hectic spec (especially in multitarget fights).
Elemental (Shaman): Nukes and DoTs. Moderately long cast times and both long and short cooldowns.
Balance (Druid): Nukes and DoTs. Long cast times and a few long cooldowns. Spammy and slow, with some really unique mechanics.
All three ranged specs have basically unlimited resources and strong healing/utility, with Shadow's arguably the strongest.
Retribution (Paladin): 2H weapons. Direct physical and magical damage. Unlimited 'base' resource powering most abilities; limited 'extra' resource powering bursty damage and some utility. Generally feels like a cooldown-constrained spec with a bit of extra flexibility, not a resource-constrained one. Decent healing/utility.
Enhancement (Shaman): Dual wield. DoTs, totems, and magical damage. Unlimited resources; entirely constrained by cooldowns and procs. Some rather weird gameplay at the min/max level (totem-twisting, hardcasting), but fun for solo. Great healing/utility.
Feral (Druid): Paws and claws. Undispellable DoTs and some direct damage. Energy and combo points work exactly like a rogue's; highly resource-constrained with some procs. Historically had a very complicated, DoT-heavy rotation, but I'm not sure that still applies. Not much healing outside of cooldowns; moderate utility.
Windwalker (Monk): Dual wield. Mostly direct damage. Heavily resource-constrained; energy and Chi work a lot like a rogue's resources, but Chi is attached to the monk rather than the target. Some short cooldowns, some longer cooldowns, fairly simple rotation. Hardly any utility or healing.