How about a series of these, Hero(Main Character), Gun-user, Slasher-Wielder, etc. So, who is your favorite main character? And why? I'll include all the PSIII Main Characters so that the field is covered. And I won't use spoiler tags in here because of the warning on the topic. Now, onto my decision!
It's a very difficult decision for me. There are so many facets to consider. Aron from PSIII has the best sprites; I love the seriousness and black cape, and Ayn for the unstated literary reference, while Alis, Rolf and Chaz all fall under the category of fighting for what is right. Chaz gets big points for exercising his mind in questioning the decree of an absent divinity, but he's generally too angry for my tastes. I thought I'd vote for Alis when I started this topic, because she is fighting an oppressive king and avenging the death of her brother, but I must cast my vote for Rolf.
I choose Rolf because he chose a job to defend the system he believed in, believing that it was a prosperous one, built to serve every individual. Another vital point is that he objectively assessed Nei for what she was, a sentient being, not a monster, and was willing to stand by that assessment and defend her with his life. As the story unfolds, he finds that the system he defends is a tyranny bound for destruction, but he continues fighting, because he realizes he wasn't fighting for the Mother Brain system, but for a productive, happy way of life for himself, and therefore for everyone in Algo. His intransigent stand for his right to life wins my vote.