More voters believe David Miliband would make a good prime minister than his brother Ed, who beat him in the race for the Labour leadership in 2010, according to a new survey.
And the poll suggested that a majority of voters think that the Labour leader would fail to deliver in power on a range of issues, including flagship policies like keeping energy prices down and tackling the cost of living.
While Labour has consistently led the Conservatives in the polls over recent years, public perceptions of its leader are far more negative than those of David Cameron, prompting concerns among supporters that Ed Miliband may drag his party's vote down in next year's general election.
A YouGov survey for Prospect magazine found Ed Miliband trailing Mr Cameron by 23% to 33% on the best prime minister question. But when voters were asked who would be the best PM if Labour had instead chosen his elder brother as leader, the result was reversed, with David Miliband besting Mr Cameron by 35% to 23%.
YouGov president Peter Kellner said: "Would a David Miliband-led Labour Party be heading for victory next year, rather than the close contest that seems likely? Very possibly, but we can't be sure...
"Had he won back in 2010, he would have had to grapple with many of the same problems as Ed: reviving Labour's reputation for economic competence, navigating the tricky politics of recession and recovery, and holding together a Labour Party that has historically been fractious after losing power. We can't be certain how well he would have done.
" The real point is that this finding indicates how disappointed many voters are in Ed's performance. Millions remain unconvinced by the coalition's record and would like to back a Labour leader, but don't think Ed is a match for Cameron."
The YouGov poll showed that 60% of those questioned felt Ed Miliband was "not up to the job" of being PM, compared to 20% who said he was. By contrast, more thought Mr Cameron was up to the job (43%) than did not (39%).
Ed Miliband was judged weak by 59% and strong by just 13%, while Cameron was seen as strong by 37% and weak by 33%.
Perhaps more worryingly for the Labour leader, who has made great play of the remoteness of the Prime Minister's life experiences from those of the average voter, the poll suggested that he was viewed as little more in touch with ordinary people than Mr Cameron. Mr Miliband was seen as "in touch with my concerns" by 25% and "out of touch" by 52%, compared to 20% and 62% for the Prime Minister.
At least half of those questioned said they expected a Labour government under Ed Miliband to fail on a range of key policy priorities, including reducing the number of children growing up in poverty (50% fail, 31% succeed), ensuring the efficient operation of hospitals and schools (51%-31%), keeping electricity and gas prices down (54%-29%), improving standards of living (53%-28%), standing up for Britain in Europe (53%-27%), strengthen government finances (54%-23%), making the economy grow faster (55%-22%) and reducing immigrant numbers (64%-15%).
Only on his pledge to increasing the number of homes built in Britain each year did voters believe Mr Miliband could deliver, with 40% saying he would succeed in this aim, against 38% who said he would not.
:: YouGov questioned 1,740 people for Prospect on June 1 and 2.