I would think that JFK would be a better option from south FL (many offline opportunities in addition to mainline).

As for DFW, I would be careful about going to MSP since it seems to vary from all rj to a few mainlines. I saw the other day that the -9 is doing a few MSP-DFW flights now. Not sure how it is to the other bases but I understand that there are a lot of commuters out of DFW.