Pena, all day and all night.
The key here is what foulballz caught-- somebody decided to play the 19-year-old Pena at big-league SS with ratings in the mid 70's across the board. And the 20-year old Pena with ratings in the high 70s, and the 21-year-old Pena with ratings averaging 80... you get the point. You can't use Pena's career stats to calculate his bad play rate.
If you look at his defensive stats at ML SS just since he was at or near his current ratings (about 900 innings), he's at zero +/-, and the same fielding pct as Branyan, about .975. Branyan is +18 in a bout one season's worth of innings. So Pena will only give up about 20 plays a season to Branyan, which is 10-12 runs, which is way, way less than their offensive difference.