For healing/cleansing, I use Shift+1-5 while mousing over dudes in the raid frame. The healing macro it triggers on the characters that on healing duty will use the @mouseoverui modifier. (Though at some point I think had them click instead, to fully select the dude, before casting the healing spell. It seemed more reliable for some reason...)

In addition, I also use the numeric keyboard for healing. Hitting 1-5 on these buttons will make the healers select my current main and heal him right away.

I put all my characters in an "Active Target Group". Then I have some buttons to cycle through them if I need to switch a character to the "Healers" ATG. All characters in the "Healers" ATG will respond to Shift+1-5 for mouseoverui healing, and numpad 1-5 for main heals. Characters in other ATG will keep doing what they're doing. Assisting and casting dps spells, for instance.