Its like asking if you prefer 4th year Dak Prescott or 9th year Dak Prescott, obviously you prefer the more seasoned player.
Romo's 2014 season was his 9th year starting! In a vacuum, its a no brainer that I would want 2014 Romo at the helm. Experience will be great for Prescott, as he has shown he can be a gunslinger. Romo had high interception years and learned to be more careful, but at the same time efficient. Thing is, he was a gunslinger since the start. I fully expect Dak to continue to progress, hopefully he accomplishes more than Romo, he only needs one more playoff win to match him.