Yeah, Heathrow Express makes sense if you're ending up near Paddington but otherwise I don't really understand it. If there are a couple of you with luggage, get a car and it's door-to-door. Otherwise take the tube and save a bunch of money. I go to London a lot and mostly take the Piccadilly Line or sometimes a cab at off-hours or from inconvenient locations. But I honestly don't understand why the Heathrow Express would be interesting outside of a narrow range of circumstances.