Lol so many choices, think I might need to just play the first 20 levels or so of zerker, bst, wiz, but dont need to on cleric I mained that back in 99. Get a feel for what each would bring to my main grp and see what would be best fit for my play style. I still lean towards a dps cause i feel that a shaman should be able to keep my sk alive just fine.
If your SK is like top tier gear a Druid or Shaman can handle the healing but for me getting to 110 and the gear needed to reach that level I needed a cleric. The group damage of the new expansions is what makes the difference between no cleric or cleric. Fast, constant group healing on AE damage- clerics own that space. Single target and some emergency group heals Shaman and Druid are great. I'd recommend you take a cleric if you want to take on top tier content, Mearatas named don't take my tank down first (Sk 310k hp, 6800 AC), normally is the other toons after the tank get's charmed charmed, or a big AE dot, and often the cleric saves them over and over where my druid could save them once- at a push twice. If the dot lands again inside 90 seconds, or runs for 4-5 ticks the druid / shaman just can't keep up.