For a large and very busy airport I like Beijing Capital Airport. It's brand new and is really easy to go through. Heathrow always feels too crowded and there are too many people sleeping on the seats (they occupy two or three for themselves) and there always seems to be a lot of slovenly-looking people lazing around waiting for flights. Then there are too many dingy, narrow corridors connecting terminals. Beijing airport, on the other hand, is big, doesn't feel crowded, is easy to get around, has nice shops, cafes etc and overall is efficient and business-like.

I also went through LA and would say it's too much like Heathrow. It seems Asian airports are best.