Right now, KC is better. Even before being injured, JG was getting frustrated, and it was starting to show. Not his fault, our OL is simply a sieve against a defense of this quality.
But generally, JG is the better QB. Not taking anything away from Keller, he's playing very well. He hasn't taken all the sacks and near-sacks, and he looks calm and confident. Throwing it well, as a result.
Let's just don't jinx him and get him blasted, too. No one plays well with a jack hammer repeatedly pounding them in the face.