Never did get a chance to try STN for flights to LON, but LHR has been so easy and painless for us (not to mention some very nice non-AA lounges), that I can't imagine STN could be easier.
Cheers.
That is a remarkable statement about LHR and utterly inconsistent with my experiences there. I usually breathe a sigh of relief when the wheels lift off (usually at least 45 minutes after leaving the gate)