Le Sok
It depends on what you are looking for. The only full Boeing bases now are LTN, BFS and NCL. I can only speak for LTN
Luton has the most number of routes, most 737 crew and as an airport is not as busy as STN or LGW.
However you are close to head office and many people choose to live quite a way from the airport.
If you are planning on visiting family on a regular basis in Europe it is probably the easiest and most convenient for getting home.
Any more questions PM me