Avoiding the rush hour is a very good idea and therefore LHR with the arrivals lounge makes more sense.

If you want to sleep then why is Wifi important? Anyway note that although the UK arrival time is early, it will already be afternoon in HK, so even if you stayed up until 3/4am HK time (evening UK time) to have the meal service you should be sufficiently rested by the time of arrival.

If taking the tube is not beneath you then the Piccadilly line would be better for (the southern side of) Hyde Park.