I stayed at BKK Novotel 4 yrs ago, and traffic is definitely a consideration. The hotel was great, and while the office was only 3 miles away, it would take 45-60 mins to drive there. So, stay where you plan to be.
Tip: when making reservations, there is (was? usd to be?) a tremendous difference in price depending on who books it. It's a lot less expensive for locals. Example: my stay in BKK Novotel. TA quoted $195/night. Local office booked it for $80/night.