I agree too, LHR is my favorite airport.
Yes, it is not surprising at times to see T3 filled with US- bound flights, but in the early mornings, it is quite diverse. In shorter T3 tier, it was pure AA while on the longer one, closer to the main part of the terminal, I saw Thai, Gulf Air, Singapore, Emirates, the list goes on and on. Eventually, I saw some Virgin Atlantic 747s as we were departing for the USA. This was late summer '01, so things might have changed.
Oh yes, for any Oneworld Emerald/ sapphire members: You must check out the AA Admirals club in T3, not only is it nice and spacious, but it offers one helluva view. It was from there that I saw all of those aircraft. I swear, we were about 50 feet away from a Singapore Airlines 747-400. It was then that I really appreciated the size of that plane.
However, BAA needs to refurbish the airside part of terminal 3. Up until right past security, it is nice, but after that, it could use some refurbishing.
Also, the other terminal I have been in is T1. I thought it was pretty nice and modern and offered a good view of the action.
LHR is a great airport, and I cannot wait for T5 to open.
Give me a break, I created this username when I was a kid...