Commuting to and from Puerto Rico will probably take a full day in each direction. Most of the junior/reserve lines I saw only had 2 or 3 consecutive days off, so I dont think it'd matter which base you're at because all of the northern bases would be very difficult to get to PR and back in your time off. But to answer your question, Billings is the most commutable base of the northern bases. And no, you cannot pick, but you can list your preference on the bid and they do their best to accomodate your requests, or so I'm told. You can bid Florida, you might get lucky, if not they just use your next choice down. FLL is most senior. Hope this helps.