I think they're both okay. Not anywhere as good as Alien or Aliens but not so bad they're bad. I thought Prometheus was a better film overall than the last two movies in the series.
I may be a bad person for this but I liked Alien^3 because it killed off Newt. I have a serious dislike for children in movies and I think Aliens would have been a stronger movie if Newt was a cat or something.
Who can confirm whether Aliens: Colonial Marines ever was a priority for Gearbox? Their outsourcing reveals otherwise across the board.
If you believe the unconfirmed anonymous Gearbox employee Reddit rant, A:CM was never a priority for Gearbox who were purportedly focusing almost entirely on Borderlands. Seems almost fraudulent to even have the Gearbox logo on the thing since it seems like most of the game was created by other studios.