I can't really advise if you should switch or not. I will note that, if you do switch, who you should fly on depends on where in the NY area you live. Long Island/Brooklyn/Queens? Delta and American are good choices, though skymiles obviously isn't all that great. Also, Delta does seasonal JFK-ATH nonstop. NJ? United is your best shot because of fortress Newark. Manhattan and the Bronx, you could reasonably argue any of the three.