From a survey published by Public Policy Polling, a Democratic polling firm:

The most epic possible 2016 match up at this early point would be between [Hillary] Clinton and Chris Christie. She leads him just 44-42. But our poll indicates getting the Republican nomination could prove to be quite a challenge for Christie. Right now Rubio leads the GOP field with 21% to 16% for Ryan, 15% for Mike Huckabee, 14% for Christie and Bush, 5% for Rand Paul, 3% for Bobby Jindal, and 2% each for Susana Martinez and Rick Perry.