Without knowing your budget, it's hard to give a reccomendation, but...
I transit SIN 4 to 6 times a year. Our prior favorite was either the Swissotel or the Raffles (at the Stamford), mostly the Raffles, because it was quiet and superb service.
The Raffles is especially pricey, though.
Lately we've been staying at the Pan Pacific. Call it the PanPac and you'll sound like a local. The price is about half for comparable levels of service, and the last several times we've been there, there was active renovating in progress at the lower levels. So we've switched to staying at the PanPac and been just as happy, for less.
Since you were considering the Raffles, you probabally won't get sticker shock from reserving a room on the Pacific Floor. Quiet floor, impeccable service, you will be wisked upstairs for personal check-in as soon as they know who you are. And since the drinks are free in the afternoon and evening in the special Pacific Floor lounge, you can even save money with no bar tab. It is worth every penny for the travel-weary.
All the best, James