Originally Posted by ajnz

UA flies from Terminal 3, so by default I'd assume they would use the SQ KrisFlyer Gold lounge - which as mentioned by N227UA does not have restrooms or showers, but you can usually get a seat easily and it often has reasonable food. The SATS Lounge in T2 does have restrooms and showers, but it's almost always crowded whenever I'm there (prior to flights to HAN & DEL) and the food has little variation.

Both close overnight, although the SATS lounge does tend to stay open later than it says (it officially closes at 1am IIRC, but I've been in there til just on 2am).

I'd echo trooper and go for the transit hotel if you want decent rest.