Thought I might revive this since we've had a few more since.
Conservative:
1965:
Heath - We now know what Powell was like. Maudling was generally poor. Interestingly, however, Geoffrey Howe nearly voted for Enoch Powell - who was then known as a free-marketeer.
Over the next thirty years the gap between me and [Enoch Powell] was to be driven even wider - first by race, then by Europe and, finally, by Ireland.
1975:
Thatcher/Howe*
I might have been worried by Thatcher at the time, but Heath had to go. Second round self-explanatory.
1989:
Meyer See username. I suspect Geoffrey Howe, despite being Leader of the Commons, voted for Meyer: he is decidedly ambiguous about it in his autobiography, and indeed nearly ran himself.
1990:
Heseltine/MajorHeseltine for the usual reasons. As for the second round, Heseltine would have split the party; I like Hurd, but he would not have made a good party leader and probably would have lost 1992.
1995:
MajorObvious: Europe, plus John Redwood is awful.
1997:
ClarkeNot sure what to make of his alliance with Redwood. Needless to say, most Redwood supporters voted for Hague (Margaret Thatcher personally called them all). It is probably better for Clarke that he didn't become leader during the early Blair years for no one could have beaten him.
2001:
ClarkeAs above; IDS speaks for himself.
2005:
Clarke/CameronTough one as I rather dislike Cameron (how can anyone like him?); but I'm not sure Davis would have been a good choice.
2016:
Crabb/MayCrabb was supported by Ken Clarke and the like. More a protest vote than anything. Obviously not supporting Andrea Leadsom.
2019:
Stewart/Gove/HuntStewart for obvious reasons until he pulled out. After that it was Boris, Hunt, Gove and Javid. Gove is the most impressive of the lot. Hunt in the members' ballot simply because he isn't Boris.
It may be worth mentioning that in the 1970s I would have been on the right of the party, and now I am on the left. I believe Thatcherism was necessary, and the right solution (mainly) for the times. In today's terms I am not terribly radical, and I dislike the antics the right is fond of.
*A little known fact is that Ken Clarke voted for Howe in the second round (he was his PPS as Solicitor General).