Kim Kardashian is not a star in any sense of the word, has little acting experience, and is pretty much a reality TV hack. It should definitely NOT be her.
Megan Fox is an okay choice, whatever people think she's not really a bad actress, the question is, is she really the right sort of actress for such a role?
Allison Carrol is English, she's the person who does all the motion capture and everything for Lara Croft in the games, and she has gymnastic experience, as well as the right look for the role. She's easily the best choice of the three, provided she can get the acting right.
Overall though, the actress has to be English since the character is also English (Angelina Jolie is a great actress and I really like her, but whoever cast her originally in the films should be shot). She also has to have good acting experience, the right sort of physique and athleticism to handle the role, and have some experience in similar roles. Personally, I'd say Keira Knightley (oooh, controversial). She fits pretty much all the rules I just listed and she's a great actress, so she could probably pull off the role quite well. For the same reasons I'd also have Rachel Weisz as a choice, again, she's a great actress who fits those rules perfectly
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So yeah, I say either Keira Knightley or Rachel Weisz.