I generally think Eternum is still the best AVN out there, but I will admit one thing: Kei is a better written protagonist than Orion. Orion is not completely characterless, but he has a very "straight man" personality. He's the stock image of a "good guy." With the exception of what happens to him in chapter 7, he kind of stays the same throughout the whole game, and his dialogue and responses are very predictable. He's a good dude, no doubt, but not a super unique dude. Kei on the other hand actually has emotions and expresses his feelings in each situation, and has his own way of handling things and responding to things. He is his own person, far more than Orion is.
That's my piece. Eternum is generally the best AVN out there, but Kei is the best AVN protagonist, not Orion. At least in my opinion.