you can do both! (on a mac at least) I remap caps lock to escape using keyboard prefpane, then use karabiner to make it ctrl if used with another key. press it

you can do both! (on a mac at least) I remap caps lock to escape using keyboard prefpane, then use karabiner to make it ctrl if used with another key. press it by itself, escape. press it and a, ctrl-a perfect!