Daily calories.
I think it's too easy to slip up if I do a weekly count. Shuffling calories from one day to the next doesn't seem like a good idea to me. Once a day is gone, it's gone, and so are the calories I just counted up/burned whatever.
I try to do my best every day to stay under, if only by a handful of calories, as long as I'm under, its ok.
Right now though, gotta go burn off 92 calories - myfitnesspal is telling me I'm over... yikes!!