As expected: Lotsa fun!
My personal opinion:
Both movies are total bombs - ridiculous plots, terrible acting, incompetent direction and so forth.
Ghosthouse is the one that's more worth seeing even without the riffs. If I didn't know any better I'd say it was filmed as an attempt to do a horror movie spoof - which failed. Never before and since I have seen a bunch of characters BEGGING TO GET KILLED so badly as these nincompoops! Seriously. There's one scene especially that will have you facepalm so badly your ancestors will feel it in their graves. The situation:
Some kids receive a weird message over radio, so they travel to the origin of the signal - an empty house - to "solve the mystery". The first guy just got killed (by the ghost, which the others don't know) and a girl got attacked by a (real, not ghostly) insane jokel with a meat-cleaver. At this point to them it has to look as if the insane guy also cut the guy's throat.
So of course they split up into groups again - one in the house, one drives some miles away to listen to their radio (why they don't do it right in front of the house is never really explained) and they leave two girls in a van in front of the house. One of the girls is catatonic and pretty much knocked out, the other's friend tells her to lock themselves in the van and stay put. After all there's an insane axe-wielder out there and stuff. The *very* next thing she does then is leaving the unlocked van with the knocked out girl alone in it on her own, because she hears a dog bark...
Future Force ... Oh my. A gritty scifi movie playing in a dystopian society that looks suspiciously like the 80s turned into a bad metal video. I have yet to grasp it completely...

As for the riffs - I found the Future Force to be the funnier one. Ghosthouse is by no means bad, but FF has more zingers in it imo. But that's sure a question of taste. If you don't like jokes about how an actor died, because you consider that to be in bad taste then you might want to stay away from riffs of a movie with Carradine in it. (to put it as tasteful as possible: He died while enjoying some
Erotic asphyxiation by himself, lost consciousness and ended up strangling himself).