For me, this discussion is about flying to the UK with London as my ultimate destination. That being the case, there's little difference between LGW and LHR. If anything, LGW is less crowded and less of a hassle ... especially on the return leg since LHR trains and airport security can both be a real circus on Friday mornings. I couldn't care less about duty-free perfume options, nor could I care less about hanging out in some lounge. By that point in the week, I just want to get home with as little fuss as possible --> which generally makes Gatwick the more attractive option.

If my destination is elsewhere in Europe, then I'm far more likely to just take a direct flight there and be done with it. As someone traveling ex-YYZ, there are tons of options. While I do like flying with Westjet, its current FF program just doesn't offer enough incentive for me to endure an avoidable connection just so I can stay on their metal, whether that's in LHR or anywhere else.