[Jon Chalk]

I always drive in D, whereas my wife mainly uses B and switches to D on motorways and dual carriageways. Use whichever you are most comfortable with. I don't think efficiency is affected as much as by other factors (wind, rain, cold, etc).

I have found the same; D for long-distance cruising and NSL roads, B for stop-start stuff, but don't really stress about changing exactly as the road changes.