WASHINGTON (AFP) - The 2016 US election might be a full three and a half years away, but that is not stopping pollsters from asking voters who has the early presidential edge. And the advantage goes to Hillary Clinton.

The recently retired secretary of state and former first lady would handily defeat any of three leading potential Republican candidates, including New Jersey Governor Chris Christie, the Quinnipiac University poll said Thursday.

The blunt-talking Mr Christie came in second in the poll, well ahead of fellow Republicans Marco Rubio, a first-term senator from Florida, and congressman Paul Ryan, who was Mitt Romney's running mate in 2012.

"Former secretary of state Hillary Clinton would start a 2016 presidential campaign with enormous advantages," said the polling institute's assistant director Peter Brown.

"She obviously is by far the best known, and her more than 20 years in the public spotlight allows her to create a very favorable impression on the American people."

Mrs Clinton topped Mr Christie 45-37 per cent in the poll, bested Mr Ryan 50-38 and trounced Mr Rubio, seen as a Republican rising star, 50-34 per cent.

But Mr Christie, who was recently snubbed when he was not invited to the upcoming Conservative Political Action Conference, outperformed the other two Democrats in the poll, edging Vice President Joe Biden 43-40 per cent and comfortably topping New York Governor Andrew Cuomo 45-28.

"Although some Republicans don't think... Christie is conservative enough for their taste, he runs best of the three Republicans tested," Mr Brown said.

"He obviously is doing better than... Cuomo, despite other indications of anti-Republican sentiment."

Mrs Clinton, 65, is the early frontrunner in part because of her ability to attract independent voters.