As a Redskins fan, I'm going to try my best to be objective. Right now, I'm picking RG3 to be the better QB. I'm basing my pick on passing performance data against teams with top 20 pass defenses, both of which are limited for these 2 quarterbacks. I picked teams ranked 1 - 20 in pass defense to provide a somewhat useful amount of data - neither of quarterbacks faced enough pass defenses in the top 10 to make any arguments.
Here is Luck's gamelog:
http://espn.go.com/nfl/player/gamelog/_/id/14874/andrew-luck
Luck has played against 7 teams with top 20 pass defenses. The remaining 9 of the Colts' 16 games were ranked below in 20 in overall pass defense.
Luck's performance against teams ranked higher than 20 in pass defense:
Jets #2 in Pass Defense (0TD, 2INT) - Loss; final score 9-35
Green Bay #11 in Pass Defense (2TD, 1INT) - Win; final score 30-27
Chicago #8 in Pass Defense (1TD, 3INT) - Loss; final score 21-41
Buffalo #10 in Pass Defense (1TD, 1INT) - Win; final score 20-13
Detroit #14 in Pass Defense (4TD, 3INT) - Win; final score 35-33
Houston #16 in Pass Defense (played twice) - (4TD overall, 0INT overall) - 1Loss and 1Win
Overall performance of Luck against Top 20 Pass Defenses: 12TD, 10INT, 4W-3L
Average ranking of Top 20 pass defense faced by Luck: Rank 11
Strength of Colts schedule: .441
What about RG3? RG3 played against 9 teams with Pass Defenses ranked higher than 20. The remaining 7 of the 16 games were played against teams with passing defense ranks below 20.
RG3 gamelog:
http://espn.go.com/nfl/player/gamelog/_/id/14875/robert-griffin-iii
RG3's performance against teams ranked higher than 20 in pass defense:
St. Louis #15 in Pass Defense (1TD, 1INT) - Loss; final score 28-31
Cincinnati #7 in Pass Defense (1TD, 0INT) - Loss; final score 31-38
Pittsburgh #1 in Pass Defense (1TD, 0INT) - Loss; final score 12-27
Carolina #13 in Pass Defense (0TD, 0INT) - Loss; final score 13-21
Philadelphia #9 in Pass Defense (played twice) - (6TD, 1INT) - Win and Win
Dallas #19 in Pass Defense (played twice) - (4TD, 1INT) - Win and Win
Baltimore Ravens #17 in Pass Defense - (1TD, 0INT) - Win; final score 31-28
Overall Performance against top 20 Pass defenses: 14TD, 3INT, with a record of 5W-4L.
Average rank of Top 20 Pass defense faced by RG3: Rank 12
Strength of Redskins schedule: .494
Judging by these overall numbers, RG3 had a better TD to INT ratio than Luck against similar Top 20 pass defense teams. At this point, I have to give the nod to RG3 as the better passing QB based on passing performance.