I don't carry a defensive knife. Just a tiny little Swiss-Army type miniature thing for cutting string or opening packages or tightening a loose screw.
If I were to carry a defensive knife, I think I'd want one that incorporates brass knuckles, so that if I were grappling with and adversary and couldn't get in a good position for an effective stab or slash, might be able to punch OR just rub the hard knuckles part on his joints or pressure points.
The pic below isn't quite ideal, but close. I'd prefer the blade to be double-edged, a bit shorter at around 3", and the brass knuckles should have little very sharp spikes on them to discourage the opponent grabbing them.
I carry this little guy horizontally at 11 o’clock. It’s accessible with either hand. It’s gonna be nasty if I have to use this as a last ditch. It’s a shivworks clinch pick I have modified. I carry it in a darkstar gear belt wrap sheath.