It depends on how good of a deal you're getting. If you can get either one for the same price, you might as well get the Boss sway bars. But I'm guessing the GT sway bars you're talking about are very cheap, and if that's the case you might as well get them. The difference in performance is unlikely to be worth the difference in cost unless you frequently track this car.
Base 2012 - 3.5L EcoBoost V6 swap (from '14 F150), MT82
435whp 510wtq Tuned by MPT Performance