Perfect choice for what? The perfect choice to ruin McCain's campaign? As you correctly pointed out, he lost an election to a dead man. He was largely unqualified to be Attorney General, and everyone knew that he was only appointed AG because he lost the Senate race and Bush was throwing him a bone for being a good party guy. He's generally regarded as a pretty poor AG.
More importantly, though, no one likes him! McCain needs to distance himself from the Bush administration, not embrace it.
Although you don’t like Ashcroft, many conservatives like him. Whom do you think McCain should choose?