The thing to consider is any potential allergies you may have. I know someone who had a bad allergic reaction to PVC in direct contact with her skin. She had gotten a PVC harness and ended up with a severe rash everywhere it touch her. This is something that you can only find out by testing it though, be it a patch test (allergy tests do this) or by just trying it and seeing what happens. Unless you are one of those who is picky about all your toys being phthalates free, you should be fine. While yes the skin is porous, you will have sweat and oils coming out of the pores during harness use which will assist in preventing anything form getting in.

I personally will only buy leather ones, but that is because I am a fan of leather. The life span of leather is much longer than most PVC when properly cared for and as far as I am concerned feel much better against my skin.