I always carry a couple of good knives with me, but I have lately gone on a utility knife kick. I'm not sure I want to carry one, but I definitely like having them around the house for opening boxes.
I don't think I've found the perfect one yet, but I do have some a like quite well.
The Oknife Otacle Pro is my favorite. It is small and very slim, but provides a good grip. The blade is completely covered, so I can use hook blades without worrying about exposed edges. The mechanism provides one-handed deployment with excellent safety. There is a neat little clip that works well and doesn't get in the way.
The mechanism is actually very good, but it gets terrible reviews. That's because it desperately needs to be lubricated and it comes from the factory dry. Mine was pretty much unusable until I sprayed it down with ToughGlide. Now it's one of the smoothest I've used.
My second favorite is the Nexland Sliding Utility Knife. The mechanism is very clever. It involves just a few pieces of titanium with no fasteners or springs. It should be pretty much indestructible. It's easy to use with one hand. Changing blades is simple and quick without tools. It also gets extra points for preventing the blade to drag along the track when it slides.
My honorable mention is the Screwpop Ron's Utility Knife 3.0. The mechanism is incredibly simple, but it works beautifully. I can deploy it one-handed, although it takes some practice. Changing blades is obvious and easy. There is also a magnet that can be used to attach it to things. The price is low enough that you can keep several in strategic locations around the house.
It is also worth pointing out the Outdoor Edge Slidewinder, which may be the best choice for the average person. The mechanism is more complex than I prefer, but it works well. There is a spring that retracts the blade as soon as you touch the button, which is a nice safety feature. It's a little bigger than the others, but still small and handy. There's a decent clip. There is also a slotted and a Phillips screwdriver.
I have also discovered some annoying limitations along the way. I put Lenox Gold blades into all my utility knives, but I've run into several that don't work with them, or with many other standard blades. They frustrate me.
The Oknife Otacle (non-Pro version) uses a different mechanism from the Pro that requires holes through the central axis of the blade. That rules out most utility blades.
Milwaukee Utility Knives are among the best, but the Compact Slide, which I wanted for its relatively small size, will not work with blades that have more than two notches at the top. I couldn't believe it and ended up taking it apart, but it really won't accept them.
The Manker UTI Edge is a nicely minimalist design, but it is just a tiny bit too short for a lot of standard blades. A fraction of a millimeter difference would have solved that problem. I also have some concerns about how well its lock holds.
Has anyone else gone down this particular rabbit hole?
I've been carrying a Milwaukee Fastback for a couple of years and it's great. I haven't missed having a full sized folder. I do have a SAK in my lumbar pack but haven't much needed the cutting blade. I'd like to get one of these sometime, which uses a utility blade but gives you the full cutting surface length and weighs just 0.9 oz:
https://www.litesmith.com/ultrafire-knife-firestarter/
It's on the expensive side though, so I've been ok without it.
I've played with a few of those keychain sized utility sliders and didn't like them, but the Ultrafire above is a "fixed blade" and even has a tiny ferro rod in the blade cover, for outdoor firestarting.
Some people are big fans of this. I tried a knockoff and found it too hard to operate, but knockoffs, you know.
https://www.quarktool.com/
I have a Quark. It is probably the smallest and thinnest possible utility knife, but I agree that it's just too awkward for casual use. I worry that it would be easy to cut yourself while trying to get the blade in or out.