Bit of a different flavor between the two. Aliens movies are horror. Riddick is action with some scary scenes. You never think "oh, Riddick is about to die", it's established that he's gotten out of bad shit on the regular and this is just another Tuesday. And honestly, half of Riddick 1 and 3 are with him playing the role of the alien.

Now, an Aliens v Riddick crossover sounds badass. He once again gets stuck on a planet with things that want to kill him, survives (as he does), and gets somebody (Ripley) to pick him up for one reason or another. At some point, they tag team some aliens. Wouldn't be a cinematic masterpiece, but entertaining at least.

actually it's a teacup

Aliens is more similar to Pitch Black, but it's a fair comparison, and, yeah, Aliens is the better movie.

Part of it is the cast/writing. Can you name any other character in Pitch Black besides Riddick? LOL.

Aliens - Ripley, Newt, Bishop, Burke, Hicks, Hudson, Gorman, Apone, Vasquez.