system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien Franchise] Why would you keep trying to domesticate Xeno's after you have the Ripley "clone"?

I know it was the dream of the Wayland Corp. to somehow domesticate the Xenomorphs into a perfect bio weapon, but after cloning Ripley in Alien: Resurrection, didn't they have something better; a human with enhanced hand/eye coordination, seemingly improved speed and strength, increased aggression responses, and bonus acidic blood! 
Rather than an organism they can't control the spread of (see any Alien movie, comic, game), they got an enhanced human that wants to fight, and may be able to understand Xenomorph behavior or biology in a way we can't. They should find out what's different in her DNA, and then work to make those changes onto more suitable subjects (colonial marines) to create a better soldier.
gpt
A human will never be perfect. But they already have the perfect killing organism. A Xenomorph is superior to Ripley-8; it is faster, stronger, and is a more efficient killing machine if used properly. 

They needed to extract the Queen from Ripley; the enhancements were pure coincidences. Ripley may have been more bloodthirsty, but she still cared about humanity. It also ties into psychology: to make the perfect colonial marine killing machine, you need a psychopath; and given the amount of time Weyland-Yutani spent trying to extract a Queen from Ripley, the company would need to keep working time after time.

Even then, when will they get a perfect killing organism? At what point will it be perfect enough to kill upon command and restrain itself? When will the Xenomorph DNA work against the company? So many factors that tie into ethics (and we all know Weyland-Yutani has none). They just want one thing: a controllable beast. But tying humans into it will draw unwanted attention from other factions. They'll see the company as a more powerful threat that now showed everyone it is not bound by ethics or morals. It is considered better to use a killing machine that is known for being a killing machine (and efficiently eliminate current threats) rather than bastardized humans and Xenomorphs into attracting attention from other factions (which would increase the work needed to win).