I'm actually going to say Alex Smith. In 2005 we had arguably the least talented roster of any team in recent history. Physically, Alex and Aaron Rodgers are very similar players. Prior to Smith's shoulder injuries they both had pretty strong arms, both are fairly mobile. Both are smart and accurate passers. It's impossible to know whether their respective careers are a product of the environment they were placed in.
Rodgers got to sit and learn behind an all-time great, had offensive consistency and a talented roster when he finally took the reins. Had Smith been drafted by Green Bay instead, he could be the MVP and Rodgers the embattled QB being traded.
The fact that we cannot know this, and the fact that we are getting the #34 pick and a high pick in 2014 in return for Smith (plus 2 very successful seasons) makes him the right pick in my mind.