No direct experience with the folding Sting, but I have several fixed blades of that model. AG designed the original Sting to be a double-edged knife that had some utility outside of stabbing. In that, he was successful. For a dagger, the Sting is actually pretty useful. In the folding model, as it comes from AG, the upper edge isn't sharpened, but you still have the same basic dagger blade shape with its issues of wedginess. If you go with one of the two Russells, the grind of the spearpoint will give you greater utility for things like slicing, IMO. That blade looks very similar, in fact, to the old Benchmark Ninja which was designed by Blackie Collins. Despite the goofy name, it was actually a damned good little fixed blade utility knife. Since AG Russell distributed the last of them a couple years ago, it wouldn't surprise me if that is where the inspiration for the spearpoint blade lies.
I own a bunch of AG Russell's knives, and none of them are junk.
OTOH, I also own a bunch of Spydercos, and none of them are junk either. I don't have any experience with this "compression lock." All my Spydercos are conventional lockbacks.
I don't own any linerlocks anymore and the only framelock I own is a Chris Reeve Sebenza, which is a substantially more expensive knife than any of yor choices above.
