Heathrow T5 lounges are a mixed bag. The Concorde Room is the nicest, although last time I was there my champagne glass was so dirty I sent it back and they forgot my food order. The First Lounge can be like a zoo, it's best to find a seat in the terrace, although they now have seats with high backs at the window, which feel more private. Galleries North and South are so busy, it feels a though it would be quieter to stay in the public area in the terminal but of course, no free stuff. By far the best is T5B lounge, often quieter and so if travelling long haul I usually head there, as flights depart from B and C gates. The Aspire Lounge is very poor, not worth the price of a visit.
Changi has some great lounges if flying One World Alliance carriers. The Qantas First Lounge is excellent, with table service, the Qantas Business Lounge is okay but gets packed. The BA Lounge is pretty good. The Bar, their First Class area, is windowless and dingy, not pleasant apart from the premium drinks. I haven't yet tried the Qatar lounge but will on my next trip.
In Hong Kong recently, I visited the Qantas Lounge, acres of space and very good buffet food. I also went to the Cathay Wing Lounge, table service and light and airy. By far the best is The Pier. Excellent staff, superb bar and great food. It's good to know that some airlines still value their customers enough to provide excellent lounges.