I slept in Paramaribo, Surinam airport but they had locked gate (like malls) and my company was a missionary family. Pretty sure no critters, tho they had access thru gates. That was 40 years ago! Bed was wooden slat bench, so I used my clothing. It was a LONG night.
SIN Changi airport--cleanest if you get stuck. That was about 6-7 hours. Last time there we stayed awake but had club access, so much more comfy. Plus we got to have chat about w/Aussie who was a wee bit tippled. Still a long 9 hours. Slept like babies SIN/NRT.