I typically carry a SAK primarily for the tools, and a small fixed-blade just for the blade. The SAK is razor-sharp and will cut most anything in a pinch as long as I'm careful, but if I have to grab for something sharp in a hurry (cut my way out of a seat belt in a car wreck, put something between me and an angry furry thing, whatever) I want it to be ready for service by the time it clears my pocket. Right now there's a CRKT Plan B within easy reach, which has a curved handle that slips nicely into the hand and a crappy little sheath that I can flick off with my thumb as I pull it out of my pocket.
When I ride my bike I typically have the smallest of the Ka-Bar Law Enforcement knives within easy grabbing distance, but not in a pocket, because pockets can be hard to access while riding. Either that or the Plan B would be a more effective tool than any folder I've ever owned if I ever had to slow somebody down by punching a blade into a sidewall in order to effect a safe getaway from a traffic "situation."
In the office I sometimes compromise by toting a small assisted-opener which I can still deploy one-handed, just not quite as fast. Life continues to confront me with a surprising number of situations in which I need something sharp and don't have both hands free.