No way is Alien 3 better than Aliens.
I'll agree Aliens' plot - at its most basic level - is a total cliché, but it's at least coherent and delivered effectively. Now, I love Alien 3, I really do, but as a movie it's a mess. The only bits that really shine on a critical level are the funeral scene and Ripley's death, they're both very well done. But a lot of the rest feels muddled.
But that's not the biggest problem with Alien 3. The biggest problem is it has no genre. Alien is a horror masterpiece, Aliens is an action masterpiece. Alien 3... Well, it's not scary, so it's not horror, and it's fairly slow, so it's not an action movie. It's not really drama, it clearly isn't romance. I guess a thriller maybe? Although even that's debatable. It just doesn't know what the hell it is, and so it kind fails at being a film.