I trust the guy that cuts my hair more than any of the above. In the end, they're all politicians.
Still, it's the Congress's job to make the laws, and the Exec's job to carry them out. Congress definitely needs to put down in writing what's permissable, especially considering the legal and political ramifications. That way, every interrogator will have a known legal standard to work with, and every Congressman can be held accountable if the practices are too harsh or too ineffective.
"Leaving it up to the President" is a losing proposition for us and our CIA agents. Bush won't be in office forever.
Every Congressman held to account? Do you mean like they were for September 11? They are not held to account for their negligence as a body, they only surface to hold everybody else to account, usually after the fact, usually to say who went too far or not far enough, depending which side of the issue makes them look right and just.