What a funny poll!
In my wallet, there is a Vic Executive. On my belt in a pouch is either a Vic Soldier (4 blade, Alox), a Tinker, or a Mechanic - oh, today, is the Soldier. In my right rear pocket is a Spyderco Delica. When I was at work, I had a Case penknife (CV) in my watch pocket as well.
I guess I have to say that if I can only carry one knife, I need to put on more clothes!

Seriously, though, both styles have their uses (even though I don't dig the Buck 110 much). When I go out exercising, I usually have a Spyderco clipped to my shorts. When I go out hiking, I usually have have the Mechanic on my belt b/c of the pliers - I can pull thorns from my dog with it. Day to day, I usually have both on me. Different uses.
I grew up in a house where traditional slipjoints were the rule. Lockbacks were tiny, slender little things with 2" blades for watch pockets and Sunday suit pants. Real work meant a big jackknife, stockman, trapper, or a sheath knife - and we made most of the sheath knives we had, and they were all carbon steel. I hated scout knives - that clumsy, awkward blade didn't really seem designed for real serious use. Didn't have a point on it, for one thing, it was the only one you had, and you had all that other crap in there that weren't very good tools and weren't very useful. If you need a screwdriver, I thought, get out the toolbox and get a proper screwdriver! Got a very painful cut while putting an edge on another scout's stupid scout knife, and that clinched it. I had an emotional, gut reaction to that blade shape for years afterwards - hated them.
Well, time marches on, and I was living in Louisiana instead of my beloved desert southwest, and my carbon steel pocketknife was struggling mightily to survive the humidity. I was riding a bike a lot, and discovered a need for a compact tool kit that didn't ride in the trunk of a car or truck bed. I got a Vic Tinker, and stopped worrying about rust. It was an improvement over the scout knife, to my mind, due to the small secondary blade. I had yet to discover that carrying several knives was an expedient answer to making up your mind about what to carry.
My karate teacher had a Spyderco Delica, and I loved it, but I was too poor to buy one. Got another, less expensive one-hand opener lockback, and have been hooked on them ever since. I've got a lot of traditional slipjoints, but I've got a bunch of single-blade lockbacks, too. They kind of take the place of a traditional small sheath knife for lots of things. With modern designed locks, they're supposed to be as tough as one. I don't know. I've never pushed mine that hard - I get out a sheath knife if I really need one.
So that's how I ended up with a nice, slim lockback in one pocket, a traditional slippie of some description in the right front pocket (where it belongs, gosh darn it!), and an SAK or two, all in the same pair of pants.
So, I don't think I can pick what the best thing is. I use my SAK a lot. But I use my lockback, too. Hmm. I could probably get along easier without the lockback, just grab a sheath knife instead. Not much replaces the utility and unique adaptability of an SAK (or heavy, fat multitool lol). But if I could only have one knife at all, and these were my two choices, I'd have to pick a lockback for being able to take on any cutting problem, and a small toolkit to deal with other stuff.
Lockback. Spyderco Delica, stainless, for me.