The term "sweating" is a misnomer. Any pipe carrying cold water will condense moisture on the outside of the pipe if the relative humidity in the room is high enough. Probably for historical reasons, this phenomenom is termed sweating, although clearly the water is not coming from inside the pipe (unless the pipe leaks), so the proper term is condensation.
I live in humid New England, and all of the pipes in my basement (some copper, some PEX) used to condense moisture on the outside. This got old, so I wrapped them all in insulation, problem solved. PEX without insulation is not quite as bad as copper without insulation, since the PEX provides a small amount of insulation, but not enough by itself.
I live in nebraska, and have pex in my dirt crawspace. My main 3/4 cold line sweats like crazy when it gets super humid here. Not to mention the water meter does too. I have the plastic manabloc manifold in my wall behind my fridge, but that never sweats at all. just in my crawlspace