My stays:

Hyatt - Orchard Road, easy walk to shopping and food courts, very happy with stay

Hilton - also on Orchard, a bit more modest, but you'd get lounge access
Conrad (with Hilton points) - Marina Bay, lovely property, excellent lounge, a bit quieter area than Orchard Road. Still, there is shopping across from hotel as well as several restaurants in walking distance.

IGH - Intercontinental in Bugis Corner area. Has an excellent lounge but you'd have to pay to get it. Again, there's shopping and restaurants near by. It's a bit less hectic than Orchard Road.

SPG - Sheraton is across from Hyatt. I have not stayed as reports of property haven't enticed me to go there. There are now additional properties in Singapore.

Of the places I've stayed, I prefer Hyatt, Conrad, and Intercontinental. Hotel standards are high in Singapore and you are spoiled for choice. In the end, don't overthink it. Look at where you have points or where you'd like the lounge. The Hyatt, IC and Conrad lounges are all comparable in quality but based on your status you'd only have complimentary access at the Conrad.