Avoid Mercure Simson! We booked the hotel because we read decent reviews on the internet, but those reviews are old. We stayed Jan 6-13, 2007, and found the hotel to be dirty and unfriendly. You can read my review at:
The island itself is great and the people friendly. Our experience at the hotel was so bad that we wanted to get away from the hotel as much as possible, so we rented a car for the entire week and it saved our vacation. They have the car rental desk right at the hotel and is very convenient. You can easily go beach hopping one day, then go to Philipsburg for duty free shopping another day, and then drive to Marigot for a the local market.
We liked the island and could go back again, but would definitely stay away from Mercure Simson !