I have lots of pex laying around. I think it's on par with PVC for flex except the UV stability of pex is less than half of PVC. So, I use PVC. I can leave it out for years and years without issue. PEX, only lives for 5 years tops in the sun. I literally deal with UV stability every day for my job. I'm constantly telling people to put UV rated split loom over cables. Lol. I love PEX, but not for this application.
Eta: I leave my PVC in the sun for 10+ years and it isn't breaking. PEX, 5 years and it's breaking into