I think the Pitch Black/Chronicles comparison suffers from the same thing as the Alien/Aliens one, being that the two movies pretty much had completely different genres. In this case, subcategories of sci-fi.
In Pitch Black and Alien, we have more of a horror setting. We have an ensemble of characters with no clear star of the show. Riddick was a mysterious character, but he wasn't the apparent focus of the film; with Ripley, she really didn't stand out from the rest of the cast until they all got killed off. In both movies, these groups face alien horrors they cannot understand, and as a result, get mauled. We get our flagship character through process of elimination.
Now, with Chronicles and Aliens, the horror seeps out. Significantly more action than their predecessors. Riddick's Badass certification from Pitch Black lingers, and he is clearly the star of the show through and through. A little less so with Aliens, but Ripley's experience with the Alien sets her apart from the marines, and things get filled with bullets by everybody. Here, the protagonists survive their ordeals and live to kick ass another day.
TL;DR - I liked both movies equally because I have difficulty comparing movies of different genres, preventing me from arbitrarily picking one over the other.
