Don't know how long reserve in these places are these days. But probably not too long. I was however based in both LGA and SJU at one time or another. Plenty of crashpads at both places. Don't know about MIA. As for commutability, it really depends on where you live. LGA is quite easy, as far as options go. But when the WX hits and/or the controllers feel like showing their clout, it can get ugly in terms of getting there on time.

SJU is easy if you live in NYC or MIA. Direct AA flights out of JFK all day long. But expect to ride the jumpseat on the A300 (NOT comfortable) maybe 70% of the time. Those flights are almost always packed. I did it for about 6 months, and it was survivable as far as commutes go. ATL is also an option, as Delta has a few flights to "the rock." AA out of DFW also has a few, but from what I remember: full flights, and there is also quite a bit of competition for the jumpseat there.