I preferred clicking when playing a holy priest: selecting targets on my raidframes (whether with click or mouse-over) and then (when I already have my cursor over the raidframe) using keyboard bindings to cast the actual heals just felt weird.
Instead I had everything (except for rarely used spells and CDs) assigned to mousebuttons - left button "Heal", middle button "Renew", right button "Greater Heal", Back button "Prayer of Mending", Shift+left button "Flash Heal". Ctrl+Shift+left button "Binding Heal", Shift+Right Button "Dispel", ...
Only used keybinds in movement-heavy situations (e.g. Alysrazor), otherwise my mouse hovered over the raidframes (Grid + Clique) the whole time and movement was handled with WASD.
On dps specs I prefer key bindings.