My two cents worth, having left my boat for 3-4 mos at a time many, many times up and down the
Caribbean:
Leaving on the hook is safer than in a marina, as well as far cheaper.
Marinas are easy pickings for low-lifes; you have to be more organized to steal from a boat afloat. I've never had any problems with theft at
anchor. I lock up the obvious things (dinghy and outboard). I've always had someone there look after her; either a
liveaboard I've made friends with and trust, or a professional caretaker company.
The two you mention plus Rodney Bay are the most typical destinations for Atlantic crossers. (Off topic hint: If you ever want to see
Barbados, do it as your first stop because it is hard to get to from the Windwards.)
My favorite places to leave a boat have been the south coast of Grenada and Simpson's Lagoon on Sint Maarten. Both are perfectly safe and secure.
Simpson's Lagoon: it's not hurricane season, and I've spent months afloat there while refitting and never seen any conditions I worried about. Anchor just over the line on the French side up near the Witches Tit. Keep to the French side or the Dutch will try to make you pay a fee for anchoring. Buddy up to some of the hundreds of liveaboards in the Lagoon and you'll soon find someone to caretake your boat.
It is definitely the #1 place in the
Caribbean for kit. You can't beat the prices or selection at
Budget Marine and Island Water World, not even in the States. If you need any professional
repair work, FKG
rigging is pricey but very competent, and Maintec, next door, can't be beat for friendly, competent
wood or glass work (tell Roger I said Hi). It is easy to fly from there to anywhere, and there are no
customs fees.
Grenada: I prefer Hog Island and have spent two hurricane seasons on the hook there, however for boat-watching go next door to Mount Hartman Bay. There is an excellent husband-and-wife team there who will watch your boat, air it out each week, check the hawse, etc: contact Mark Sutton at
islandreams@caribsurf.com. They did a great job for us.
If you really want a marina, check out Clarkes Court Bay. They are very out-of-the-way and safe, and when I was last there there were liveaboards on the docks who made sure it was very secure.
http://www.clarkescourtbaymarina.com/