i've tried to plan out menus but it just never works for us. i know in theory it should make things a bit easier for me but in practicality it doesn't seem to be so. while i can do a daily menu from time to time more often than not we're an "at the moment" kinda house.
I do a combo of things, depending on how busy I am or plan to be. I am a big fan of freezer cooking, so there is always something I can pull out in a pinch or plan to have if I know I'm not going to have time to cook something fresh. My preference, though, is to plan my meals by the week, but life doesn't always allow me to do that, so I just go with the flow.