3.15:1 will be the better for daily driving and fuel economy. The 3:55:1 will result in faster acceleration (if you can get the power down) and slightly less fuel economy.
After lots of research, I went with 3.15 gears because I plan on boosting in the future. The 3.55 with some extra power apparently leads to lots of spinning in the low gears with the 3.55.
There's also 7 forward gears with 3 overdrive gears. I really see no need for the increased gear ratio, which would just lead to more shifts.
I believe that the 0-60 of the 3.15 can actually be quicker due to longer gears/in torque band longer, while the 3.55 is shifting.
I did a lot of research on this and went with the 3.55. Mainly because that is what I noticed the majority of people go with on the automatics who tried both in person at a dealership.
I have seen a lot of videos of people racing 3.15 against 3.55 and the difference is completely unnoticeable. In theory, the 3.15 is faster on the top end, 3.55 is quicker in the initial acceleration.
The coyotes torque is higher in the rpm range, so with 3.15s you spend a lot of time in daily driving outside of the power band and the car feels super sluggish/slow. My 2016 GT came with 3.15s and I ended up paying to have them swapped for 3.55s.
It's not even a question that the 3.55s are better, and honestly you're not even going to sacrifice much fuel economy unless you spend most of your time on the highway
I went with the 3.55, 3.15 is just too long in the tooth. On MY18 F-150 I had 3.31, when I ordered MY22 F-150 I went with the 3.73, much better choice. Applied same logic when ordering the stang. Plus the convertible is heavier. Can use the extra punch.