The latest survey by the nonpartisan Pew Research Center also finds that interest in the presidential campaign has risen notably as candidates have begun to enter the field. Two-thirds of voters said they were thinking about the campaign, up 8 points in two months. But fewer than 1 in 3 say they are thinking "a lot" about presidential politics this far ahead of the November 2016 election.
Among Republicans and Republican-leaning independents, 57% say they have an excellent or good impression of their party's candidates, while among Democrats and Democratic-leaning independents, 54% do, the poll found.
For the GOP, that's a notable switch from this point four years ago, when only 44% said they had such a positive view. The field at that time had only a couple of well-established political figures in it. Partisans on both sides have a more positive view of the choices than they did in the run-up to the 2004 election, when about 4 in 10 rated their parties' candidates as excellent or good.
The survey asked for specific impressions of Hillary Rodham Clinton and six GOP presidential hopefuls -- Jeb Bush, Marco Rubio, Scott Walker, Rand Paul, Ted Cruz and Mike Huckabee.
Bush, the former governor of Florida and brother and son of former presidents, was the best-known on the GOP side, with only 12% of Republicans and Republican leaners saying they could not rate him. He also had the largest share with a negative impression, 35%, compared with 52% positive.
Walker, the Wisconsin governor, was the least known, with 36% not able to rate him. He also had the best ratio of positive to negative opinions, with only 17% unfavorable compared with 46% favorable. The numbers reflect the good start Walker has had in his as-yet-unofficial campaign, but also the fact that he has yet to establish a clear image for many.
Conservative Republicans are more likely than moderates or liberals to have opinions about the GOP field. They are a bit less positive about Bush than are moderates and liberals, but not dramatically so, with 37% of conservative Republicans and 34% of the party's moderates and liberals having an unfavorable view of him.
Both Walker and Rubio, the Florida senator, get significantly more favorable opinions from conservatives than nonconservatives in the party -- a potentially important factor in a party where conservatives dominate the primary voting.
Clinton's ratings have declined, but she remains extremely popular among Democrats or Democratic leaners, with 77% having a favorable opinion of her. That's down from 86% last summer, but still a much higher number than any of the Republicans garner among their partisans.
Among the public at large, opinion is closely divided on Clinton, with 49% viewing her favorably and 47% negatively. Her ratings are down most sharply among Republicans, 17% of whom now say they view her favorably.
The youngest Democrats, those aged 18 to 26, were least likely to have a positive view of Clinton, with 65% viewing her favorably. Among other age groups of Democrats, about 8 in 10 had a favorable view.
Although some liberal activists have pined for alternative candidates, 81% of liberal Democrats viewed Clinton positively, compared with 74% of conservatives and moderates. And despite her potential appeal as the first female elected president, male Democrats were about as likely to have a positive view of Clinton as females.
By contrast with Clinton's generally positive ratings among Democrats, Vice President Joe Biden's star has faded. Only 58% of Democrats and Democratic-leaning independents viewed him favorably, and among voters overall, 39% have a favorable view compared with 48% who view him unfavorably.
The Pew survey, conducted May 12-18, polled 2,002 adults, including 1,497 registered voters. The margin of error for the registered voter sample was +/- 2.9 percentage points.
For more on politics and policy, follow @DavidLauter on Twitter.