Clinton, the former secretary of state and U.S. senator from New York, leads Sen. Paul of Kentucky, 49 percent to 41 percent, and former Florida Gov. Bush 48 percent to 40 percent, a Quinnipiac University poll released Friday indicated.
Vice President Joe Biden trails Bush 44 percent to 38 percent and lags behind Paul 43 percent to 39 percent in hypothetical matchups, the poll found.
Clinton had a 52 percent to 40 percent favorability-to-unfavorability rating, off from an all-time high 61 percent to 34 percent in a Feb. 8 survey by Quinnipiac University in Hamden, Conn.
Results indicated Biden had negative ratings, 37 percent to 44 percent. Paul had a positive rating, 32 percent to 24 percent -- with 42 percent saying they didn't know enough about him to form an opinion.
Results indicated neutral attitudes about Bush, with both favorable and unfavorable ratings at 29 percent. Forty-two percent said they haven't formed an opinion.
Even though her favorability rating dropped, Clinton "remains the queen of the 2016 hill at this point, but the wide gap between her and some of the leading Republican contenders on favorability may be closing, as her overall favorability has taken a hit," said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute.
Results are based on a survey of 1,419 registered voters conducted May 22-28. The margin of error is 2.6 percentage points.