I am in the extreme, extreme minority about this, but I actually vote for Chris Johnson as rookie of the year, and not one of the QB's.
It is extremely rare that a QB can come in as a rookie and have their team be successful, and both of them, especially Ryan, have done fantastic jobs. That said, they haven't been the reason their teams are winning. Ryan has certainly had the better season of the two, but it doesn't take an MVP to hand the ball off to the 2nd leading rusher in the league. Flacco has that Baltimore defense.
The two of them have managed games this year and let the team around them make the plays and win. Ryan has made some plays here and there, but both of them focus more on not messing up than being the playmaker. I think if you took them off their respective teams, both teams would still have success. However, I can't say the same about the Titans and Chris Johnson.
The Titans offense depends on the QB to manage the game also, and let the running game and defense take over. As a rookie, while carrying most of the load on offense, Johnson ran for over 1,200 yards, at 5yds a carry, and 10 total TDs. He also had 43 receptions for 260 yards and a TD. They use Lendale White on the goaline, and Johnson still had 10 TDs. You take him off that team and they are nowhere near as successful.
He means more to the Titans than Ryan or Flacco mean to their teams, AND has put up better individual numbers at his position.