Keep in mind that the standard Rear End gears are 2.71 with the manual, but 3.31 with the Auto. They put the 2.71 in the manual to improve the gas mileage, but it's still 2 MPG less that the Auto,. Plus most guys on here want to change the 2.71's, which will drop your highway MPG further.
But the no one buys a Mustang for the MPG.
Depending on were you live, there may not be that many manuals to choose from.
The Automatic transmission in the 2013 Mustang, has 3 modes. "D" which is really economy, "S" sport shift for more aggressive automatic gear selection, and a fully manual gear selection mode of all 6 gears. The torque converter locks up in 4th, 5th & 6th, thus no slip and the good MPG ratings.
I only drove manual cars for the first 30 years of my driving. Even when I was married with kids I special ordered a Dodge Aries station wagon with a manual.
But I love the Auto in my Mustang.
Ignore this post it is completely wrong.
First of all the manual and the auto both come with standard 2.73 gear ratio in the US.
Second, no the auto doesn't at all beat the manual in MPG either. Look up anyone with a manual who records they can get a solid 34MPG highway with the 6-speed manual.
In my opinion, get the manual, regardless of traffic because I deal with traffic sometimes too, you are engaged with the driving experience, and it takes skill.
Times may not be as consistent as the auto, but that isn't important at all what so ever, what's important, is you're having fun.
And for the last time, the manual doesn't get less than the Auto, EPA isn't always completely accurate. You control what you want your MPG to be; shift below 2.5 RPMS every time I guarantee you'll be getting good numbers.