MIA- How could it not be my favourite? So much variety! Turkish A340s, Virgin 744s, Iberia A319s, Air France 733s (yes, as in 737-300), Tampa DC-8s, United 772s, Lloyd Areos Bolvianos A310s, American A300s, Continental BE1s, Northwest DC10s, Alitalia MD11s, Fine Air L1011s, airTran 712s, Delta 722s, Varig 763s, TAM A320s, and just so much more!
JFK- Same variety as MIA, just more European and Asian carriers and less Latin carriers.
FLL- Great airport. At first, it seems like your average American airport that serves 15M passengers a year with the Southwest and Delta jets all lined up, but then you see the Air Jamaica A320s, the Condor 763s, and the South African Airways 744s, and it's a whole different story.
MPB- One airline, three flights a day, and the most incredible landing approach of any airport in the US.
LAX- Variety once again, and to me, that's what matters.