Personally I'd say shaman + monk in any situation hehe, but I'm biased as that is the combo I've been playing since day 1.
But on regular servers, you can get a cleric merc on the monks account, and a warrior merc on the shamans account, so you have all the bases of the group covered, tank, heals, slow, dps.
You could manage with an sk shaman if you wanted to go that route, and replace the tank merc with a dps merc, but it depends on your play preference. SKs are also not as good of puller as monks imo since the lack any form of lull.