MPs believe that being decisive is a more important trait in a good prime minister than principles, honesty or intelligence, according to a poll.
More than three quarters of the 158 who took part in an academic study chose it as one of the top three requirements for being a successful occupant of 10 Downing Street.
By contrast, fewer than a third (32%) put being honest among their priorities and intelligence was picked only by a minority (49%) of the cross-party group.
Being principled was identified by 68% in the study by the Department of Politics and International Relations at Royal Holloway, University of London.
Margaret Thatcher emerged as the MPs' choice as the most successful prime minister since the end of the Second World War.
But the Tory - who spent 11 years in Number 10 and died last year - came only very narrowly ahead of Labour's Clement Attlee, who presided over the creation of the NHS.
Winston Churchill - whose wartime leadership often secures him top spot in polls of the best prime ministers - came only fourth when judged solely on his 1951-55 term.
Sandwiched between the immediate post-war premiers in the poll - which did not include David Cameron - was Tony Blair, who won three consecutive general elections from 1997.
Fifth spot was taken by Harold Macmillan, followed by Harold Wilson, Sir John Major, James Callaghan, Sir Edward Heath, Sir Alec Douglas-Home and Sir Anthony Eden.
Bottom of the table was Gordon Brown who was scored just 3.3 out of 10 - less than half the rating of Mr Blair.
Of the MPs who responded to the questionnaire, 69 were Conservative, 67 Labour, 14 Lib Dem and eight from other parties.
Those from the two largest parties were generally more supportive of PMs from their own side - with the exception of Mr Heath, who was ranked higher by Labour than Tory MPs.
Dr Nicholas Allen, senior lecturer in politics at Royal Holloway, said: "It's not surprising that MPs perceive Thatcher, Attlee and Blair to be the most successful prime ministers.
"Attlee and Thatcher both presided over fundamental shifts in British politics, while Blair, like Thatcher, was a proven election winner.
"When it comes to winning big majorities, David Cameron still has much to prove."
He said that while she came top, Baroness Thatcher remained a divisive figure - attracting the widest range of responses.
The survey was sent to all 650 MPs in October as part of class project involving third-year undergraduate students.