I've been flying the same route for the past 20 years.
LAX to LHR to either GLA or EDI
First 10 years Virgin and ANZ. These past 10 BA.

The past 3 years I've been going back and forth about 4 times a year. About a month ago, I was stuck in Heathrow for 12 hours waiting for a flight from London to GLA.
Now I know that all airlines are the same and at this point not even looking for "customer service" since any excuse NOT to give good service.

But I need an alternative to Heathrow.
In your experience - should I shoot for Gatwick? Maybe Amsterdam? Just accept that to get to Scotland I need to suck up Heathrow