I think what it comes down to for me personally about McCain is that even though I disagreed with a lot of his politics, I do genuinely believe he cared about the country and the people in it, and generally speaking he did what he honestly thought was best for them.
We can criticize the relative purity of every politician until we’re blue in the face, but honestly the one overriding characteristic I think it’s fair to demand of every elected official is that they’re honestly working in good faith for the betterment of the country. As long as that’s true I have no deep-seated issue with them.