I was given a Cold steel spartan and love the thing for its weight and feel, not sure if i like there marketing, i want a plane edge the is around 3 inches or more, dont really know much about grinds and what they have to offer, and handle material is not a big issue as long as its not super slick, lock types i have used are lock backs and liner locks have only have a few liners fail but that was cheap doller store blades not sure about the other kinds of locks out there are, i like flippers and steel types are kinda a new thing for me, i like AUS-8 and i have used a 420HC from buck and loved them other then that i dont really know, oh and i hate serrations and thanks Rycen i will be careful
I wouldn't worry about a high quality liner lock, they are just as reliable if done right as any other lock type. In terms of strength, cold steel's triad lock (basically a back lock with a stop pin), Benchmade's axis lock, and spyderco's compression lock (looks like a backwards liner lock, but really is completely different and VERY strong) definitely are tops. In terms of ease of operation, axis and compression locks win.
Blade grinds are very much personal preference. A hollow grind gives you a very thin blade behind the edge, but a thicker spine. A full flat grind will be just that, flat from the spine to the edge. Full flat grinds are known as good slicers. Saber grinds start part way down the blade, keeping the spine thick nearly all the way to the point, gaining strength but sacrificing slicing ability. This is a VERY simple explanation of these grinds but will give you an idea other cutting performance of a particular knife before you use it.
Blade steel is also very subjective, but the aus-8 and 420hc you've used is pretty low end. In your price range, look for s30v, 154cm, vg10, d2, zdp-189, m390, elmax, and a few others. Any of those listed steels will blow aus-8 and 420hc out of the water in edge retention, but many will be more difficult to sharpen.
Handle materials vary greatly by price and application, but g10, aluminum, and titanium are common in knives in your price range. Aluminum and titanium are pretty self explanatory. G10 is a layered composite made of glass fibers and resin. G10 is extremely durable and grippy.
Given your mention of flippers as well as liking the heft of your cold steel, I would recommend the zero tolerance 0350. It's a beefy assisted opening flipper with a 3.5" blade with s30v blade steel and nice grippy g10 handles. The torsion bar that springs the blade open can be removed making it a manual action flipper if you want. Can be found in either black dlc coated blade or bead blasted or stonewashed.
A light weight slicer alternative would be the spyderco paramilitary 2. 3.5" S30V blade, full sized g10 handle with excellent ergonomics, spectacular compression lock. Just a great knife, and perhaps one of the best edc knives of all time, and certainly one of the best knives around under $200.
but currently a torsion bar assisted knife is legal and i found a dealer in canada that has the 0350 for $138