Pete, just remember that if you go to an independant shop you'll have to pay a Ford dealer to re-flash your tune for the differant gears. Unless you are getting a real tune. I've driven the V6 with the 2.73 & 3.31 and bigger is better. I would like to try the 3.73 but have heard enough stories about noise to make that mod unlikely.
Do the 3.73's, they are fun. About the only way to have more fun is to add a Procharger.
Wife = 2012 Mustang V6 Premium Grabber Blue BBK CAI, BBK LT w/ HFC, Borla ATAK, MPT Tune, DSS Driveshaft, 3.73 FRPP Gears, BMR LCA's | Best = 13.5 @ 105
Husband = 2010 Camaro V6 Synergy Green Edition IPF Supercharger Best = 12.5 @ 111
Closest finish @ the line = Wife by 0.0028 seconds (4.79 inches)
Also own a 2014 Mustang GT Premium, Brembo Package, 401A, Comfort Package, Shaker Pro System, Pedestal Spoiler