I've been to London twice this year. Once to LCY on NW/KL and the other to LHR on AA.
Hands down. LCY, LCY, LCY! AMS is a much nicer transit airport for me than ORD
On departure, 5 minutes to get checked in at LCY (even if I had to explain to the check in agent where Seattle was) compared to an hour at LHR this week on AA.
Never AAgain. Next time, LCY. Cost was only about $20 more, but 20 well spent.