Parting Shot is overall superior for the reasons Halmar stated, but U-Turn does have a place on Assault Vest sets. Incineroar can sometimes run Assault Vest, as Intimidate already softens physical hits and Assault Vest lets it take on special hits as well. In that case, Incineroar is unable to run Parting Shot, so it has to resort to U-Turn.
Regulation F does have monsters like Chi-Yu and Flutter Mane, so if your teams struggles against those, you can try to use Assault Vest + U-Turn.