Really no contest, the high-end suites at the Fullerton are stunning as they are all different and make good use of unique architectural features (building was originally a post office). The regular rooms are shoe-horned in and quite a drop in quality. I stayed in a Fullerton suite which is a step down from the Governor suite and was very pleased. Much nicer than Raffles or Shangri-La (and I am fussy about hotels). Raffles suffers from being deluged by tourists with a topology that doesn't make the hotel private.

If staying at Fullerton, be sure to try their bar on the roof (former lighthouse), it has great barman who can actually make the best mojito in Singapore, and well stocked cuban cigars. The Italian restaurant below the bar is also worth a visit, try their Sicilian wines, there are some real gems not often available outside of Italy. Food is variable (pasta the safest choice). Room service does well though, and I think the Governor suite comes with dining room/kitchen.