I would choose either the Swisshotel Stamford or Raffles Plaza.
They are adjoining towers that share probably the best fitness facility in Singapore.
Lau Pa Sat hawker center
http://www.kopitiam.biz/lps.htm is nearby for inexpensive street food and Boat Quay, also in the area, has numerous outdoor full service restaurants. The river boats at Boat Quay offer a scenic, touristy, way to relax. Plenty of shopping in the area. Drop some coins in the Suntec City Fountain of Wealth. Stop by Chijmes
http://www.chijmes.com.sg/, a collection of nightclubs across the street from the hotel, in the evening for drinks.
As far as airport accessibilty, these hotels are closer to the highway than choosing something on Orchard Road. You'll hit morning rush hour on the day of your arrival wherever you go but shouldn't have any problem on the morning of your departure.