We had the same dilemma last year for DS - Judd vs DGS from Bromley. We went with DGS which DS preferred but the journey was part of the decision. He gets the coach but has to get public buses home 1 or 2 times a week after clubs which seems to be working out fine. I was happier with the coach option partly in case he left PE bags/trombone on it - a lot easier to trace than if it were on the 269 bus/7.35 to Tonbridge
As a commuter to work in London, I also know how unreliable Southeastern trains frequently are. There again, I suppose there will be lots of DCs affected.
Good luck with your decision.