One big advantage of LGW over LHR for Y/PE passengers has been that you can buy fast track arrivals at LGW for 7 GBP, regardless of status. I prefer LHR on VS because of the 330 2-3-2 instead of the 747 2-4-2 on the lower deck, but being out of the airport 15 minutes after landing is a big deal vs. an hour or more slogging through LHR T3 customs.
That will be mitigated somewhat by LHR allowing electronic reading of US passports in the future, but it's still LHR arrivals...