IMHO- the top few experiences I've had so far.
- Lufthansa First Class Terminal in Frankfurt- private spa cabanas, sit down restaurant catered by DO&CO, fully stocked bar, cigar lounge (if you're into that sort of thing), and driven to the airplane in a porsche.
- Qatar First Class Lounge in Doha- overnight hotel rooms, in-lounge art exhibitions, sit down dining and vintage champagne.
- Thai Airways First Class Spa in Bangkok- the food in the lounge is meh, but all F passengers get a 1 hour complimentary massage. Business gets 30 mins foot massage.
- Qantas lounge in Singapore- very high quality F&B, great interior design and comfortable place to get work done. going to get even better when the First Class lounge opens later in 2019.
i think SIA's lounges are generally comfortable but not life-changing, although I hope the new lounges they're doing in Singapore will raise the bar ( https://milelion.com/2019/07/05/what-can-we-expect-from-singapore-airlines-new-terminal-3-lounges/ )
And the best part is- all these experiences can be redeemed through the magic of miles and points.