Depends on the knife. Southard size & weight? I'm definitely clipping it. Traditional SAK/Kiwi/Air size? Most definitely just going in the pocket.
There's a place for both. Obviously, wearing slacks or (some) khakis with a clip is not really an option, or at least a faux pas, and so smaller clipless knives are the way to go.
edit: Oh, but also: I have on occasion found that clips can make knives MORE prone to being lost, at least in the back pocket. I recall having my Persian 75mm clipped to the back pocket of some khakis and on a few instances finding as I was sitting down that it was barely hanging on, only a few millimeters from being lost.