ATL-ORD and ATL-LGA would be the best because it would be on Eagle. ATL-DFW is not to bad. ATL-MIA will give you gray hair. I also never had a problem getting to SJU or LAX.

I have done ATL to ORD, LGA, DFW, LAX, SJU, MIA.

If I were to put them in order from easiest to hardest it would be:
ORD, LGA, SJU, DFW, LAX, MIA.