I'm not a fan of the Orchard Road shopping area, which is where the Hilton is located. To me it doesn't look appealing, but IIRC it's been renovated. Also IIRC one of Singapore's best restaurants is there, named something like Iggy's.

The StR is around the corner from Orchard and the Sheraton and Grand Hyatt up the hill. There's a new Westin (a bit like a W for business travelers) located between Chinatown and the Marina Bay Sands development.

All of these are close to a subway station. The ones that aren't would be along the far (western) end of the river, such as the Holiday Inn Atrium and Millennium Grand Copthorne.

I can't picture the IHG properties.