Any of those are solid duo's, and a lot of it depends on preference.
For myself I would stay away from the pally for a brand new duo. Pally's are great, but have low dps compared to warrior and SK. SK and warrior comes to play style. SK gives you a lot of utility tools (especially FD) and highest burst damage of the tanks, which lets you kill harder stuff on your own earlier. Warrior is a lot of fun since the revamp a couple of years ago, is an active playstyle without having to deal with mana, probably highest consistent dps, and mitigates like nothing else letting you plow through farm/exp mobs.
For the healer, assuming the tank is your main, I would avoid the shaman. Shaman's are great in the first half of tiers and buffless due to canni, but eventually fall off due to mediocre single heal out put and virtually no group option. I would only consider a shaman really with a pally as the shaman brings good single target dps and the pally makes up for group heals in exp. Don't get me wrong, shamans are amazing to have in a raid, but having played a low tier one and high tier one, but eventually you get into situations where you just can't put out enough heals alone. Druids are amazing for a duo, they are perfect quest, snipe and farm bots, allowing you to clear a bunch of spawns, evac and start again. With a tank as the other half of your duo, it would be rare that you get into situations the druid couldn't heal you through for farming/questing. Cleric is the power choice; don't fool yourself into thinking the slow of a shaman will let you tank the hardest mobs at your gear level. I can't think of a situation where a shaman would be able to keep up with healing while pausing to canni that a cleric couldn't easily heal through (duo at least). End game you won't even have to cast heals with your cleric unless you screw up or are duoing raid mobs, you just autoattack. If I were picking a brand new healer to duo with a brand new tank I would probably go druid, especially since it has the added bonus of being the least likely to get picked over your tank by a guild.
Edit: Yes if you are ok using your healer to leverage the tank into raids, cleric is the way to go.