TATL 767 have IMHO a better in-flight experience than a 777 but narrower seats. Posts on the AA forum seem to indicate a 80%+ Preference for the 767..after all, on a 777 there's superior Cabin in front of you. Negative is no OPUP Chance to First.

Last time I flew AA through SEA they had an excellent TSA First Class - Fastrack.

Remember there is no Premium Air Duty/Tax if you connect through LHR within 24 hours.

For sector fares from Singapore try http://www.zuji.com.sg/ Or http://www.airfares.com.sg