I like them equally. Though, its hard to deny that the second game improves on a lot that was flawed in the first game:
- Zero Gravity just felt like a clunky mess in the first game, I'm sorry, if you can enjoy it, then by all means do. The free-form movement in the sequel just felt so much better to handle to me in 2.
- The new necromorphs in the sequel made combat more interesting. I usually play a few, extremely long sessions at a time, and having to fight the same handful of enemies in the first game wore on me after a while.
- The scripted events were better. Looking at you, turret sections.
Not to bash the first game entirely though. The environments in 2 were more varied, but there was something in the drab brown and greys of the Ishimura that captivates me. I enjoyed the story and characters more in the first game, there were some genuinely unsettling moments that still make my hands shake a little (like that guy bashing his head into the wall), and the my favorite necromorph still remains as the Twitcher.
Now, if you were mentioning the third game versus the other two... eek.