I do not have personal experience but here's a link from a forum that has a section on SXM......and members are fanatics Traveltalkonline: Unity Car Rental ?
The only place I've rented from on St. Martin is Prestige in Grand Case and I was very pleased. It's on the French side and a great place for foodies and more laid back than the Dutch side. I'd definitely suggest it if you aren't set on Philipsburg as so many seem to be. One quick warning... as on many islands you should completely ignore traffic laws/signs and be prepared for more than a little creative driving!
The only thing more exciting than driving yourself (my last fun drive was Antigua) is taking the local stand anywhere by the road, pay much less, squeeze everyone in, music can't get louder - local Vans driven by wanna be Formula1 / Rally Car drivers who make USA tailgating look like folly.
Available on many but not all islands.......so if You have not been on a rollercoaster in ages......go for it
I was in St. Maartin is Dec. 2007. I would not drive there if you paid me. Narrow two lane roads and locals that pass whenever the feel like it. ie--Going up a steep hill with a sheer drop off to one side. I was glad we were on the mountain side and not the cliff side. Good luck with yor rental, I'll take the bus or taxi.
What John said! Driving around the island can be a hair-raising experience, if you are unaccustomed to narrow, winding roads and steep hills.
At least driving is on the right side of the road, on both the French and Dutch sides.
Buses run from about 6:00 in the morning to midnight, and can be boarded at bus stops in towns or flagged down anywhere along the roads.
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Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
Thanks for all the comments everyone. We'll be taking the bus when returning from the Heineken tent but have a car reserved for island hopping I've driven in St Martin previously, just like being home and driving in Detroit. Freewheeling fun!