When even the ( IMO ) disastrous Bkk airport ( Swampy ) was better than Heathrow, it says something. At the least Bkk airport had trolleys for passengers' carry on bags, and more toilets.
I always hated having to fly out of Heathrow on Thai Airways, as they were always at the farthest end of the very long passageways, and those walkways were devoid of any decoration, which Swampy does have.
Even the waiting area was vile, and at some stage was reduced in size so they could put in more duty free shops.
Heathrow was horrible, from the endless underground tunnels linking Underground and Terminal, the unfriendly staff, the incompetent security checking staff, the atrocious design, the congestion and the overpriced "restaurants" to the looooooong boring passageways to the boarding lounge.
I can't think of a single "pleasant" experience I had despite flying to Thailand from that <deleted> <deleted> at least twice a year for 10 years.
I suppose that if there was one thing that would have made it worse would have been flying British Airways, but at least I was spared that ultimate attrocity.