Keith Joseph of course.
People forget that Joseph actually got more votes than Heath on the first ballot, he just didn't have the 15% margin to avoid the second contest. Then at the post-ballot press conference he had to make those remarks that the working classes should be using more birth control. Apparently Heath was not even going to contest the second ballot, but stayed in and defeated a clown car of candidates.
There is no reason that Joseph shouldn't have become the Tory leader if he hadn't made those remarks (which were mis-interpreted). The question is whether he makes them later on, having kept his mouth shut for the leadership contest, and whether this or something else is enough to blow the 1979 elections for the Tories. As leader he presumably would have had the staff to prevent or smooth over these things, and he would have made an interesting PM. Of course the Tories lost those years in the second Heath government until he was deposed anyway.