I think most everyone, including myself, failed to mention FBs because they're "usually" illegal to carry & it just "seemed" that the OP was asking about folders even though he didn't say that, lol.
IMHO, the Perrin & Ronin are great SD knives. However, "senoBDEC", unless you're carrying your FBs open carry, it's illegal in Calif (FYI) & that includes neck knives. That's not to say LE will bother you & many seem to think 2" blade or less is OK, so depending on what you're carrying, you might be OK.
The Ronin's great & was specifically designed for SD. It's basically the same as the Yojimbo, but it's a FB &, of course, the handle's smaller & the blade's a little bigger, IIRC. I believe the Ronin's blade is 3" vs the Yoji's 2.75" & the handle's 4" vs the Yoji's 5", but the Yoji's larger handle is mainly to hold the blade & have a little extra hanging off the end to use if the blade's not opened.
As an aside, I mentioned that I was expecting a modded (Waved & bead blasted) Yojimbo soon. Well, it came in & WOW. The wave changes it immensely. While it's still not as quick to action as the P'Kal, it's close & just as good or better, than the waved Delica/Endura. I flipped the clip on this one, too, & now it opens with edge forward in an ice pick grip.
Having said all that, IF you really need a knife for SD, a FB is probably the best & although the Perrin Street Beat is probably considered the best Spyderco FB for SD, I'd have to say I prefer the Ronin, but that is just me (& ONLY) my opinion.
For neck knives, though, I still think the SPOT (Not the Swick) is one of the 3 top neck knives.
Interesting thread...