From a muscle development standpoint, the only real difference between chins and pullups is that the elbow flexors are in a much better position to contribute in chins. Which is also why you're stronger in them.
All else constant, it seems to me that we should be using variants of a lift involving the most muscle mass through as much range of motion as possible. Which is also Rip's justification for low vs. high bar for his squat prescription.
Pullups are a good exercise, but I can speak from experience that pullups very easily go along for the ride if you build your chins numbers, so I'd concentrate on that, first.