There are pluses and minuses to all Eagle bases.
LAX is expensive, but the Saab is relatively junior, it's a good plane, and you can transfer to the RJ when you can hold it. Remember, you can "up-grade" to the RJ from a turbo-prop, but you can't go back to a turbo-prop from the jet, so make your domicile request after careful consideration.
BOS is expensive, but the destinations are great, local hotels are outrageously expensive if you get stuck for a night, and it's all Embraer RJs. Don't stay at a crash pad run by a flight attendant named "PJ" or something to that effect, the dog isn't potty trained
Dallas is probably the cheapest place to live and it's easy to commute, It just wasn't my favorite place to fly. The airport is huge and there is alot of walking involved, but the food choices are many and varied.
I was never based in Chicago, so I don't know what it's like to fly there, but I did live there for a winter. It's cold. The Cubs are fun to watch. Commuting is pretty easy between AA and United.
Miami was a blast, but I hear the overnights are very short now. Flying in the Bahamas and the Florida Keys was great. I was there in March, and it was 80 degrees and humid, with the air-conditioning running at max.
San Juan? Yo no se. I have heard the overnights are great, St. Kitts, Antigua, San Maarten, etc. But, there are down sides. Commuting is tough and rent is high, so is the crime rate. I have heard it's a great place to work if you are single and speak spanish. Also, you have to go through customs almost every time you return to San Juan.
New York is expensive, Kew Gardens can get old quick if you are thinking crash pad, but there are lots of them. The destinations were great.
Choose wisely...