My experiences flying through BHD have so often been jaded by completely unacceptable waits for taxis, often over half an hour. There aren't that many people in the queue either - just no taxis available. This is in complete contrast to airports elsewhere in the UK with huge lines of taxis (but woe betide you if your journey is less than 20 miles!). Not what I expect of a "business market" airport.
As this problen does not seem to arise at BFS, it can be quicker to get into the centre of the city from there, despite the longer distance.