Maybe this is a new leaf in 2025 and I'll have to reconsider my shift in spend to preference CK on AA, though probably not 
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This is entirely the LHR-based GS team, who have always been the absolute best in the system, and still are. It’s the only location where the service is bar none, and the standards are high. They are excellent with personalized follow-ups and outreach, problem solvers, time and again. They've had very little turnover, with many outstanding agents with over 20, 30 years service. They train their team so well that even newer agents deliver the same standards - something that doesn't seem to happen anywhere else.
From curbside to plane the experience for GS at LHR is the best it can be in the system, IMHO - staffed lanes, proactive staff, separate club area, orderly boarding.