Been to both the FS Singapore and Raffles. Hate'em both, so I can't help. Of the two, I'd take the tourist-circus-that-is-Raffles. And I'd just take the insults from the hostile staff with a smile. DO NOT ATTEMPT TO STAY EVEN 1 MINUTE PAST THE CHECKOUT TIME!!!! That is simply not allowed at this hotel.
FS Singapore is, at best, an industrial cave. The place is so dark and depressing that I was expecting to see bats in the closet. The exterior looks like a prison.
I've had my best stay at St Regis.