Raffles the Plaza is attached to a mall Raffles City and a MRT station (City Hall). It was formerly a Westin and one of the wings have very modern rooms and Heavenly Beds. The original Raffles hotel is just across the road.
Oriental is attached to a mall Marina Square and a long walk from the MRT station (City Hall) but taxis are inexpensive in SIN. This location is quieter than Raffles City and is generally more pleasant. Cant comment about the rooms.