So much of a young QB's success is the system he plays in. Look at Matt Ryan last year. Because Michael Turner and the running game were so outstanding, and the defense was playing well enough to keep them in ballgames, they didn't ask Ryan to do too much. Watching Stafford today is the polar opposite. Detroit gives up a lot of points and they don't run the ball very well. They don't have the luxary of simplifying things for Stafford. I think he'll be okay. Same for Sanchez, but they are going to need to have the talent and coaching staff around them to be really good.
Warren Moon was pretty good. Disagree a lot with that statement Mamba. McNabb, McNair, Cunningham, Vick. Disagree about Vick Moo, he was a solid QB just never became elite. His rushing was epic you can go to any statistical site and they will show you he is well above average taking into account both factors (approximate value of 17 in 2002, 15 two other times). He was injury prone and had a short career, but he's accomplished more than Romo (approximate value 17 in his peak, might have another great season in the future but 12 is his second highest so far).
I'm talking about your prototypical QB. The pocket passer, the one that wins you championships. Vick, in that sense, was god awful.
To my previous post - I totally forgot about McNair and Moon, both were great QBs. Randall Cunningham was solid but nothing special. He had a good W/L record, but his statistics weren't what I'd consider eye-popping, but yea, I'll give it to you, very solid. As for Vick, he's a good athlete but a bad QB. He was more of a threat with his feet than he ever was with his arm. In terms of being a drop-back, prototype QB, he was basically crap.
Really, 4400 total yards, 35 TDs and 13 interceptions for Cunningham in '90 wasn't eye popping? Not really sure you remember that. He was just fine as a passer he's a guy Vick and almost all the other elite scramblers wanted to be.