For the sake of simplicity I would say SAL. All flights are international, so there is no need to transit through any part of the airport to get to your next gate. It's all in the same terminal.
If you do want to head out to the beach keep in mind there's a fee ($10 cash as best as I can remember) for US citizens to enter the country. Also, security wait times are very short to get back into the terminal, so there's little risk of being stuck waiting, especially if you already have your BP. There are multiple car rental agencies on site.
If you buy duty free at SAL I would make sure that you actually get it delivered to you before you board. The FAs suggested we board and they would bring it to us before they closed the flight, but that didn't happen and after speaking with an FA they found it and ended up handing our rum through the cockpit window.