Ideological purity is for children, who want to insist on exactly what they want, when they want it. Politics is about the practical. As a Conservative, I think it's down to Fred vs. Rudy, and the only relevant question is who can put up the best fight against Hillary Clinton and her machine.
I do like Fred very much. See The Conservative Case for Fred Thompson, by Hawkins. I also believe that Rudy is much more conservative than people think. Murdock at NRO: It's Wrong for the Right to be Rudyphobic.
Despite all the things that weigh against Hillary, I think it is going to take some fancy footwork to put her on the ropes. Is Fred up to that? Can he be expansive, vital, cheerful, embracing - or is he a grumpy old man like me?