Well, first, stay away from Dollar/Thrify Car Rental. They seem to employ some unscrupulous practices and try to hold you accountable for damage to the car that was there when you picked it up and reported it on the inspection, in a way to just extort money from you. Read these disturbing reviews, if you haven't seen them, yet: http://www.fodors.com/community/caribbean-islands/beware-st-maarten-car-rental-with-dollarthrifty-car-rental.cfm
Check here for lists of car rental companies, and read precautions re: the price of gas and trying to be taken advantage of in the conversion of Dutch Guilders and U.S. Dollars at the pumps: http://www.sint-maarten.net/st-maarten-carrental/stmaarten_rentalcars.html
Even the 'big name' car rental companies like Avis, Hertz, Alamo, are owned by smaller, independent agencies on the island, so don't be swayed by the popular names, as they will most likely not back up the practices of the smaller agencies, should you have a problem.
From the reviews I've read, most people who have rented cars recently, recommend Ace Rental, Kenny's Car Rental, Original Car Rental, Brinks, Unity and Hertz. http://www.tripadvisor.com/ShowTopic-g147346-i222-k4757249-Honest_reputable_car_rental_in_St_Maarten-St_Maarten_St_Martin.html
Pick up and drop off at airport is best, XXXXX XXXXX's what you need. Most of these companies appear to offer that service.
I wish you a wonderful vacation, safe travel, and Happy Holidays!
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