I choose none.
I choose a Harold Macmillan National Goverment
But in all seriousness, Whitelaw. It may be closer, but 1979 was the Conservatives to lose. You after all don't get an 8.1 Swing purely on who you leaders is, but because of the absolute nightmare the last Winter of Callaghan's Premiership had been (I mean, if you ask if it were 1978, I'd probobly say a Lib-Lab Coalition). So yeah, unless Whitelaw drops the ball, the Conservatives are more than likely to enter Goverment come the 1979 election.
And before anyone asks 'what about the Liberal's?', you'll need PoD that avoids Jeremy Thorpe and the mess that was his post-1970 leadership entirely for the Liberals to be able to be in any position to form Goverment, and even then, as we all know, the Liberals only had a marginal shot in 1983 in the short months before the Falklands because of extraordinary circumstances.