Both have had some great successes in their earlier careers. But Wentz's injuries were the result of stupidity and were almost self inflicted.
I remember JG eating our lunch more often than not. He's got talent.
From what I've read JG is more familiar with McVay's offensive style than Wentz.
Finally, I trust McVay in this decision. He had Wentz in his hand and chose to let him go. At this point McVay is wise enough to know which QB will work best for his team.
I would actually be happy with either of them because both seem to be more than good enough to be backups.