I live somewhere where EDI is nearer but GLA isn't much further. However being in England (just) I'm not with the local rivalries on the issue. I tend to bias EDI because the parking and public transport options are better there. I would say security is better at GLA (but it's quite good at EDI), the lounges are about the same overall, EDI being somewhat bigger and with more facilities. The Menzies staff who handle BA are efficient at both stations. Overall they are both good airports and so it's not like either are MAN. I take GLA because it's sometimes has cheaper fares and/or better timings, but it's quite marginal. So I wouldn't over-think GLA v EDI in isolation, they are both good.