Best:
-$660 Kali Audio IN-8 v2 pair, I have yet to find a valid recommendation for the price that doesn't either lack bass extension, vertical dispersion, hiss, port chuffing, and work as a package for both nearfield, balanced, unbalanced, and living room use.
-$30 Koss PortaPro, which is what got me into the audio hobby. The first time that I heard details in music that I hadn't heard before was with these headphones.
Worst:
-$500 Cowon Plenue R (Doesn't really make a difference having excellent measurments with a DAC and amp. You can't hear the difference. I tried a blind test with a friend switching between it and my phone too.)
-$2500 Genelec 7271 ***But this is from the standpoint of me paying for convenience, and the difference being small relative to the price, as it's just covering things under 60hz, and the integration with GLM and the 8260 monitors in my living room is what I'm paying for. Not the best value for output and such, but worth it to me because with how it integrates, it's the best subwoofer I've heard, and I didn't have to spend a week tweaking it only to return it and fail at getting it to sound perfectly cohesive with the speakers.