Pioneer SE-700: Best headphone I own so far. Nice detail retrieval, a good sense of rhythm, nice imaging, and nice airy sound. A little thin at times. Bass is just not there, which makes a few songs less exciting. Mids are nice and smooth, never nasally or boomy. Highs roll off at the very top but are otherwise quite nice. The sound is overall very smooth and flat. Very fun to listen to despite their analyticality. Unamped, they are unlistenable. Out of my E7 they do get better, but not as good as they could be. Driving them from my desktop subwoofer's speaker taps kills what bass they do have(as the subwoofer has an internal equalizer to keep the bass out of the satellite speakers), but makes everything else sound absolutely unbelievable.
AKG K240 Studio: Warm. Moderate detail retrieval, moderate attack and decay. Small soundstage, meh imaging. Tight, controlled, airy bass response. Liquidy mids and highs smoother than butter. Some of my denser music (such as Psyborg Corp.) turns into a disgusting mess on these. Not good for all genres. Most comfortable headphone I have ever worn.
Pioneer SE-500: Basically, everything the SE-700 is like, but worse in all departments. Had these before the SE-700s. Loved them too before I got the 700s.
KOSS K/6x Plus: First "real" headphone, got from a garage sale for $10 when I was 12. Bright. No soundstage, no imaging. Skeletal, light design makes them fall off my head easily and makes it sometimes hard to get a good seal. Very tight bass that reaches low but not very low, stops around 13 Hz. Sparkly highs that are a little bit rough. They are neutral with a slight tilt towards bright. Very well-detailed.
Audio Technica ATH-M50: I really don't like these anymore. Meh detail retrieval, meh attack/decay. Midbass hump, fairly tight low end but not as good as it could be. Absolutely disgusting midrange, heavy distortion and roughness throughout the entire range. Highs jump out at you, scream in your face, and smack you across the cheek. It's not quite harsh, but it is definitely noticeable and to be honest I don't enjoy it very much.
Audatron SH-608R (heavily modded): I took the driver off the baffle and secured it in the back of the earcup. I removed the original pads and substituted AKG pads. I messed around with the damping a lot and removed the two volume potentiometers in the earcups. Doing this made the sound airy and delightful and made the soundstage huge. They still have no imaging, however. The bass is no longer suffocating and the mids aren't boomy anymore. They're basically a worse K240 Studio, with less treble and more bass. Pretty bad but they have more bass than any headphone I have so they still get some use.
Audatron SH-608R (stock): Absolutely atrocious. Muddy bass that overwhelms the other ranges, boomy mids, no treble. Sound is very suffocating and oxygen-deprived. No soundstage and no imaging. Slow attack and decay and meh detail. Pretty heavy. Bad isolation, but better than most. Uncomfortable as sin. Thin supra-aural pads and way too much clamping force. Only redeeming qualities are nice, tough build quality and appealing visual aesthetics.
Unranked:
KOSS Reference One: Just got these yesterday. Huge KOSS cans from the 70's. The bass reaches low, the highs are sparkly and smooth, and the detail is good. Absolutely massive soundstage with good imaging and instrument placement. They're heavy and built like a tank. They squeeze hard and isolate better than any headphone I've ever heard, and they don't leak at all. They seem to be extremely analytical... not sure how to rank it yet though.
