In terms of design alone?
Dark Ops Knives, with their Interceptor E&E as a special mention. But they're ridiculously expensive.
Overall, I like Buck, specifically the Buck Nighthawk. $60, comfortable grip, almost effortless to manipulate, absolutely perfect balance. When there's a Buck Nighthawk around when I get bored, I find myself holding it (sheath still on... that part's important!) in a reverse grip with my index finger on the finger groove for the little finger, and just pulling back. The knife flips a full 360, and I catch it in the exact same position as it was before it flipped, without moving my hand at all (just closing my fingers around it as it completes the flip). It's also very sharp, and holds an edge pretty darned well. And for that price, by the time it loses its edge, you can actually afford to just buy a new one.
I also like knives by Takeshi Saji, and Kanetsune from Japan, purely for their artistic nature. I have a Takeshi Saji Yo****sune, which has a snakeskin covered grip and sheath. As I say to everyone when I bring this thing up: 'It's part Asian, part Texan, just like me!'
....The board censored that...... .....The censored part started with an s, and ended with a t, so you can figure out the name of the knife and look it up if you want.