It'd be hard to find either that's not been raced. They are out there but few n far between....But, I'd go for a Camaro 2SS w/1LE package.

Pass on both:  the 2014 Mustang GT came with a 6-speed Getrag transmission which is the weak link for that vehicle: lots of complaints and subject to class action lawsuits.  As for the Camaro SS, expect electrical gremlins to plague the vehicle.  Definitely avoid the automatic transmission version as it was paired with a V8 (L99) which came with cylinder deactivation (susceptible to lifter/engine damage over time).

And then of course because both have V8’s and meant to go fast they were probably beat up on - you’d be inheriting wear and tear (even imminent damage) from the previous owner.

I would take the Gt. Not a fan of the Camaros looks.

The ls engines are much better than the modular engines, so if those are your choices, Camaro.

Ideally? Third gen Camaro, they go forever even with hard use providing you have the 700r4 (do the vette mods as they're cheap insurance) & a 350. For the price you'd be paying for either of the newer ones you most likely can drop a fresh crate engine & tranny in a rust free example, any repairs would be far cheaper as well. My 87 went almost 200k of HARD use until I blew the tranny, the engine still ran like a top though.