Jack - Simon Pegg; he looks quite different from the Jack in the game, but why deny this possibly-amazing movie one of the best nerd-actors known to man? Simon Pegg is the best kind of leading man, one we can all easily get behind. He can do comedy and drama well, and can do an American accent. He’s the perfect choice for the guy who leads us through Rapture.
Andrew Ryan - Geoffrey Rush; although he’s not been in a “nerdy film” before, I think he’d fit in quite nicely as the ruler of Rapture. He’s great as historical figures and men in power, yet also men who are maniacal and mentally unstable. I think he’d be the only choice for Andrew Ryan.
Atlas - Ewan McGregor or Colin Farrell; I feel they are both strong choices and fit well into the “born-leader” role, although Atlas himself would say otherwise. You’d want the leader of a revolution to be intimidating yet likable. Strong! Colin Farrell is more of a “if-we-can’t-get-Ewan” pick, but that’s not to say he isn’t a strong, likable actor. He can use a gun and fight, and he’s got his share of notable acting chops. They’re both good choices.
Dr. Brigid Tenenbaum - Scarlett Johansson; the obvious choice, I think, would be Carla Gugino because she’s always in movies adapted from comics. She’s like the go-to actress for a role like this. But she over-does it. I think a better choice would be Scarlett Johansson. She can act in dramatic roles well, she can pull off a foreign accent, and she’s not the obvious choice. This is very different from the roles she’s done before, yet she could totally fit!
Little Sister - Chloë Grace Moretz; this girl is tearing up the movie world right now. She has both blockbuster and indie hits under her belt, and this movie could be a great next step. Hit Girl wouldn’t be the only Little Sister in Rapture, but she’d be the one we all cared about most.
Those are my 5 main picks, and I think arguably the 5 characters that would be the selling point for the film.