I'm finding the [target=focustarget] macro to be the better solution for my 3 shaman. However, because of the tiny bit of lag, when i target something to attack and then see something walking towards me, i change target and quickly start to cast, I find that my slaves are briefly stuck on the first target I have, which means they both cast at the first target, while my main casts at the one I want to attack. Can lead to some interesting fights. But I'm sure it's something I'll get used to as time goes by.

I am also finding that for most fights, they are over either before the mob gets to me, or within a couple of hits, so moving around isn't that important. Frost Shock/Frost Bolt will also help with that later on, slowing the mob down to create more time to kill it before it reaches you.

Best of luck with working out what works best for you.