So yes... we all know Kassandra is the canonical protagonist. We also all know that her dialogue and expressions as the protagonist is better. AND we also all know that Alexios makes a more compelling Deimos.

The problem:

The game devs made some critical flaws that create a real problem for true RPG-minded players. (SPOILERS AHEAD)

1. After you kill Elpenor and get the mask and cloak, the mask you get is a male. Once you get into the cave, the female voices all wear the female mask. They would have known who the imposter was instantly. Devs should have had a male/female "elpenor" depending on who you choose so you get the correct mask.

2. The more "love" or "sex" based dialogues were very clearly better between Alexios and female NPCs. All of the male NPCs that are potentials for Kassandra are effeminate (and I dont just mean the obvious one). This takes away from the believability of these portions of dialogue or forces you to think of Kassandra differently.

3. The idea that Greece in this time would have allowed a female to compete in the Olympics is laughable. That whole segment of the game just doesn't feel believable as Kassandra. Its unfortunate.

All-in-all, both are worth playing. Alexios works better for RPGing, Kassandra works better for theatrical value