3-box PVE class combo questions

Looking at setting up to 3-box and would like to have the core elements covered, so was planning on going holy trinity. I'm planning on running instances etc, and was hoping to level in instances rather than quest since I've leveled 3 characters to 70 already, pretty much done most of the quests. As far as instance grinding with only 3 chars, doable? is the XP too slow to make this worthwhile? I figured I could always pick up an extra DPS or 2 if i way to run something a bit harder.

I've done some reading on the Wiki/forum etc regarding class combinations and the general consensus is paladin for tank by long margin, which means I'll be playing horde side (don't like any of the ally pally races). For healer I've heard that shammys are good, but, don't like horde shammy races (I like elves, sue me :P ) so it's a tossup between priest and druid for healing. My understanding is that priest is probably the easier of the 2 to box, as druid requires a bit more fiddling with the HOTs and lifebloom stacking, but was also thinking the hots give you a little bit of fire and forget healing, toss the HOTs out and your tank should be stable for a bit. Anyone with a bit of experience boxing either of these healers got any suggestions?

Also for the 3rd member, DPS, was leaning towards warlock, since the burst DPS of the mage is overtaken by the DOT dmg from lock, with me only running 3 characters while fighting elites, will take longer. I suppose a hunter might also suit well in the DPS department? Gives me some offtankage to help with larger pulls.

Thanks for any hints.

I think priest are the best healers in the game in my opion.

A warlock would add wipe protection and healthstones, and does quite nice damage. Could do fragile crowd control with the succubus. Banish and or enslave against demons in instances can be great. If you can clear an area and pull back in there you can go to town with a focus fear macro to effectively take one mob out of the equation for a sustained period of time.

I initially thought a palladin + 2 druids would be good. One resto, one feral but then thought that might be difficult to 3 box. (although I suppose if you specced boomkin instead of feral that might work.

I like the versatility of the druid - your healer swaps to tank form if he pulls aggro, your boomkin switches to healing, while your paladin gets aggro back. (bear in mind I've only got a druid to 32 as of last night - no pun intended)

I am about to get a third account as well, and I was thinking about a priest+lock+paladin setup for doing instances. Would this work, or should I try something else?