I personally prefer heathrow for on the ground stuff (lounges, getting through security etc).
In terms of Service, I found that the BA lounge at LGW is far less friendly than the ones in both T1 and T4 at LHR. But then there are as you point out more staff in the LHR environment.
With regard to cabin crew, I would say that the flights I have done out of LGW long haul are more or less the same in terms of friendlyness and general quality of crew on the flights.
BA are my preferred long haul airline for flights to the USA, Middle-East and Far-East. Although I normally use Cathay when I am flying to Australia since I rate their service as the best of any airline I have flown.