Tough one...lol....really tough one.
It really all depends on how much Hillary is willing to let power slip. If in a Obama/Hillary administration, Obama is clearly in power and has the last say when it comes to the issues, I believe that it would indeed work out pretty well. We have, atleast to some extent, the new style of Politics Obama promises with a more or less unified democratic party.
However, the way I see Hillary, she will want to have full control over everything - so, in her version of tha ticket, she'd love the do it as the current administration handles it, Bush playing the puppet and Cheney pulling the strings. In that case, McCain would definitely be the lesser evil.
On a sidenote, I think McCain is a pretty solid break from the W. Bush administration. He is certainly more capable militarily than Bush and Cheney put together (like that was hard

), and his domestic policies differ quite a bit from W. Bush.