From what I have read I would go with the tune, hands down. You may decide to swap gears in the future and the tune would be needed anyway. Just remember if you do a tune, under warranty and you have problems the dealer can tell if you have been in the on board computer. So I would suspect any engine issues, or transmission issue if you have an auto might be tough to get work done under warranty.
2014 GT Premium, Ruby Red, 6speed, 3:73 gears, 1969 Sportsroof Performance Red.