I've stayed at some of the above recently. Some comments:
- JW Marriott is a good Marriott, but the rooms still lack that luxurious feeling (enhanced standard Marriott carpet, etc.). Better breakfast buffet than the Royal Orchid
- Royal Orchid: renovation work on the Tower floors is not over yet
- Shangri-la: I haven't stayed at the Oriental or Sukhotai, but the Krungthep wing is far more luxurious than any of the American chain hotels; right next to the Skytrain. Paying rack rate at any Shangri-la's yields a number of benefits, including laundry, airport transfers, etc.
- Sheraton Grande Sukhumvit: less of a resort feel than the Royal Orchid, but a newer and slightly more upscale property IMO. Truly excellent Sunday brunch.
- Hyatt: a good property, better located for business and shopping than tourist activities.