For O/D traffic LGW is every bit as good as LHR (maybe better for some). The big difference is connecting onward; LHR has far more flights and thus gets most of the non-O/D traffic. This may get more interesting next year when T5 at LHR opens and BA may move some of its LGW flights to LHR, at least for the business destinations, making LGW that much less appealing for non-O/D traffic.