To each his own.
I happen to like pocket clip carry.
There are pros and cons of course.
Pro:
Knife dont float around in the bottom of the pocket.
Knife is 'squared away' and easily accessible.
Con:
Certain types of clips can be pocket eaters.
A knife with a clip can make it annoying to get keys out of the same pocket, that the knife is clipped to.
IMO the pros outweighs the cons, but thats just me.
If a knife dont have a clip, I install one. Like on the Leatherman Juice and the SAK below
The Spyderco has a home made custom titanium clip (though the Spyderco wire clips are some of the best in the business IMO).
The NiteIze clip on the SAK here is the best most positive retaining clip, that I have (the other NiteIze clip on the Juice is a POS, as it lets the Tool slide out of a pocket with ease. No good.). It has small 'hooks' which 'bite' into the pocket material and holds the knife in position no matter how much you move about. You simply cant drop a knife out of the pocket by accident with this clip.
It does eat pockets though. Still the clip, that I like the best. I would hate having a knife dropping out of the pocket either because the clip didnt do its job or because the knife gnawed a hole in the bottom of the pocket. Positive clips for me.
