If you are only considering the '01 snake or the '07 GT, definitely get the '07 GT because it's almost certain that a 5 owner cobra has been whored around (unless you don't mind not knowing its previous history, etc).
BUUUUUT, if you were considering a GT, I'd wait around to score a new '11 Mustang GT (if it's in the budget). Those things look very promising with the new hp/tq numbers.
YMMV