I've got a parkerized 870 and I'd wish I'd gotten the blued model, they're a lot smoother, look much nicer and scratches can easily be touched up with cold blue.
Parkerizing might be a little tougher and is a lot more rust resistant as long as it's properly greased, but it's not that much better that it makes up for the above IMO.
Edit;
Forgot to mention that the slide bars on my 870 are blued, and they have never shown any sign of rust in the rain and humidity that it's so often exposed to in my neck o' the woods, so to me that says there's really no need to put up with thick and gritty parkerizing as long as you're up to taking even minimal care of the gun.