PC, very, very definitely. There WILL be a significant difference in graphics quality (better textures, antialiasing etc.), and it's the futureproof version, with a strong possibility of mods and fan-patches. Look at the Thief community, they're still churning out quality stuff for Thief II, 12 years after the release!
I completely agree with this and would advise the same thing. They will most likely release mod tools, I have a strong feeling they might because they know how strong the modding community is and have seen what it's done to Thief 2 and Deus Ex.
And I completely agree with this
Also, the PC version is more configurable, and keyboard + mouse is always a better control scheme for a first person game.
It gives more precision and a more natural feel to first person games.