Practically or theorethically
In my opinion, these 2 theories, which everyone is discussing about, can be described as the title says. Faith being alive and glamoured as Nerissa - practical, Nerissa being alive, while Faith - dead is theoretical. I'm a fan of Nerissa being alive theory, but Faith being alive seems to make more sense - her tale is about deceit and hiding, Swineheart running more tests on the head, suspecting something wrong... Of course, it has some plot holes, but they're not that big. However, Nerissa being alive is based on emotions - there are many scenes where Nerissa is acting very emotionally and being, well, herself, as we would imagine it. Some of her scenes are heart-breaking, and she is overall very sweet. In episode 5, when blaming CM, she says "My name is Nerissa !" If Faith can put up this kind of acting, then I really don't like her. She's a very good actress then or a complete sociopath. Nevertheless, Nerissa being alive has one huge plot hole, to which I can't find a reliable answer - if Nerissa was disguised as Faith while at Woodsman's place, why "real" Faith's head has beatings on it ? Anyway, these are just my two cents. Sorry for bad formatting.