ESPN is putting on a full-court press for the statistic that they hope will replace passer rating: Quarterback Rating or QBR. Passer rating is a horribly outdated statistic, based on 40-year-old data and failing to take into account crucial aspects of a quarterback's play like sacks, running, how effective a pass was and other aspects. Still, it wasn't all bad: you could use it at a glance to see which QB approximately had a better season or game. It wasn't perfect, but it sufficed for that purpose.
ESPN's new QBR is a lot more complicated, and includes a lot of new things. Sacks, rushing yards, effectiveness of passes (8 yards on 3rd-and-9 is less valuable than 2 yards on 3rd-and-1), yards a pass traveled through the air vs yards a receiver gains after the catch: all of these things are incorporated. And all of it is weighted by a 'clutch' adjustment, which is a poorly chosen term for explaining they look at how much the pass or run helped a team win a game. If you want the full explanation, follow this link. All this doesn't mean the new rating is perfect, it's just another tool to evaluate players, as with every statistic. Interestingly, the stat is very similar to Football Outsiders' DVOA, without opponent adjustments and with a few game-charting based additions.
All that said, it's interesting to see that this new statistic values Josh Freeman pretty highly. In 2010, he was the NFL's 10th best quarterback by this measure, ahead of established players like Philip Rivers, Ben Roethlisberger, Tony Romo and Matt Schaub, though still lagging behind Matt Ryan and Eli Manning as well as the standard list of elite quarterbacks. In fact, ESPN now has Freeman ranked as the most efficient running quarterback in the NFL, though that's hardly the most important part of a quarterback's job.
The fact that Freeman does well in these rankings isn't entirely surprising, of course. According to the old Passer Rating he was even the 6th best quarterback of 2010, while Football Outsiders had him ranked as the 9th best quarterback. In fact, it seems the new QBR values Freeman a little less than other measures.
All this to say that there is now a new tool to evaluate quarterbacks statistically, and it's better than passer rating. Along with Football Outsiders' DVOA, Advanced NFL Stats' different measures and of course more traditional statistics, there are plenty of statistics to choose from to support any argument about quarterbacks.