I was very impressed with Griffin III as well, but Luck is the best QB prospect I have ever seen. And that is not an exageration. He has an absolute gun, perfect footwork, great pocket presence, and most importantly a quick release that rivals Brady/Manning/Marino.
I still have some questions about Griffin, but to me, Luck is the biggest lock to be an elite NFL QB since Peyton Manning (and in fact, I like him much more than Manning coming out of college).