I also rarely shoot in AI Servo mode, but it's very useful for those times when I need it (rapid fire action sequences - typically birds in flight). The thing to realize about the way AI Servo works is that it uses the first shot to acquire focus and then tracks from there. As a result the first shot in a sequence of frames will be less likely to be in focus then the later ones. For the same reason if you shoot single frames in AI Servo the focus will be less reliable than if you use One Shot mode.
In summary: if you're shooting single frames (as I do most of the time) you're better off with One Shot. If you're shooting machine gun bursts (particularly of a moving target) use AI Servo.