SIN and HKG would be my picks.
Being stuck in HKG is most likely due to typhoon threat, so that's a double-edged sword (but the terminal was supposedly built to withstand the fury of typhoons).
The LH First Class Terminal in FRA would be interesting, although being stuck in FRA would likely be because of Eurocontrol strike or snowstorm. People say being stuck in a snowstorm is hell, and let's face it - being stuck somewhere with a snowstorm is more likely to have you being stuck on the plane on the ground, rather than in an airport terminal. But if I got stuck in the FCT and it's frosty outside, at least there's about 60+ varieties of single malt to keep me warm (if I get that desperate).
I think the long and short of it all is that if you're going to be stuck at an airport, it's better to be stuck in the lounge than almost anywhere else.
If I didn't have any lounge access whatsoever, I think my pick would have to be SIN.