Kind of a different take here as we don't actually have one favorite restaurant. Rather, we have favorite dishes that only certain restaurants do great.
For example, if we're in the mood for 'za, we go to a particular pizzeria. If in the mood for lamb chops, only one place to go for us. Burger tonight (?), we know exactly where to go to satisfy that urge.
So in a roundabout way, I guess my answer would be "always order the same thing" since we generally go to that restaurant for a particular dish.