Top level would be SQ suites, assuming you don't want to pay for Eti-hads residence with private butler. Emirates on the A380 with showers would be most enjoyable as would Qatar with their private terminal.
Premium pricing obviously applies on the top business and high end leisure routes. Best value is on mid level leisure destinations where the pointy end is usually empty except for those burning their FF miles. As the cabin flies anyway the airline may as well get some revenue.
Thai to Bangkok and possibly on to Phuket would give you the best value. Even business class fares on SQ or Cathay from London to their home base will prove shockingly expensive, let alone first class.