The guys over at CVG have put up a comparison between the Xbox 360 and the PC versions of both Episode 2 and Portal from a graphics point of view.

Quote: "Anyway, as you can see, it's a closely fought contest with each Episode Two outing throwing visual haymakers, but the PC version has the edge (considering it's running on a machine costing at least three times as much as an Xbox 360, it bloody well should do).

One thing to note between the two Portal versions though is the difference in control. As you can see - and probably imagine - the game's puzzling antics are a lot more laid back with an Xbox 360 joypad (and less jerky), which is one of the reasons we prefer the console version over PC."

Read the Episode 2 comparison over here.
Read the Portal comparison over here.