No substantial Military. No natural resources the US will one day need to steal. Year round Tropical climate. Moderate cost of living. Low (or better yet NO) tax rate. Small population. And multiple methods of travel in and out of the country.
While I like Latin America, the US has too much vested interest there and there is too much history of political upheaval. Costa Rica would have been a great spot to buy property in...10-15 years ago...but now, that ship has sailed.