Silent Assassin whenever possible. Except achievement runs or the ocassional dicking around with a shotgun(easily my favorite weapon in the game for pure satisfaction). I like having so many ways to play through the scenarios, for a fairly linear plot, it's got great gameplay.
The stop time and kill everyone mode is rather overpowered though, even if it is amusing to wipe out a whole group of 15+ soldiers in a few seconds.
I am not too much of a fan, I get caught too easily.
USB 3.0...is blazing. Holy crap. I wish I could see what Thunderbolt was like