I might be biased, but I watch every Ravens game and Flacco is a very good Quarterback. Definitely top 10 in my opinion.
In no particular order
Manning
Brady
Rodgers
E. Manning
Brees
Stafford
Vick
Roethlisberger
Rivers
Flacco
He does sometimes hold on to the ball a little long and could do with a bit more awareness in the pocket / throw the ball away more, but he has one of the best arms in the NFL, he has good accuracy and he can scramble a little if needs be.
He made an amazing drive in the AFC Championship game against the Pats, AND he got the ball to Evans in the end zone. Evans **** up the catch that would have taken us to the Superbowl, and although we can't prove it, I reckon we could have beaten the Giants.
Like I said though, keep underrating him, works out better for us