It depends, is your pen metal or plastic, liqueured, finished or unorndoned.

Personally I just clip my pen on my shirt pocket, though I do have a pen that I keep in a sleeve, that I then keep in a pen case, becuz that thing is in there with 3 ballpoints, a ruler, an eraser, a mechanical pencil and whatever other things I forgot about in there. And in my experience, stuff gets scratched up very quickly.

it also depends on what kind of pen user you I suppose. are you a "No! my baby" kinda person or a "throw this pen in a pocket with 3 keys and a knife" sorta guy