Pros: Great sound, Comfortable, Well Made
Ive listened to the Ultrasone HFI-780, Sony MDR-V6 (MDR-7506), Grado SR80i, and the Sennheiser HD598. The HD598 wins.
The Ultrasone HFI-780 has absolutely terrible sibilance/sibilant. This is a common complaint with these cans. The 780 has better bass than the HD598, but the sibilance ruins these cans.
The Sony MDR-V6 (aka MDR-7506) are phenomenal cans, but rather boring. These are some of the most popular headphones ever made, for good reason. They do sound incredible, and they are inexpensive. Every sound is fantastic. However, its boring. People in the audio industry refer to them as flat, and flat is the perfect way to describe them. And some people love this sound, however I do not like flat headphones for overall music listening. The MDR-V6 are studio monitors, which mean they are primarily made to be used in a studio or with other professional applications where you can monitor how loud a particular sound is. These cans heavily emphasize the mids, and thats not necessarily a bad thing. Those who love acoustic music or love hearing vocals will prefer these over the HD598. Some treble and some "hissing" can be heard on occasion, but overall these are amazing headphones if you like flat sound.
The Grado SR80i are another great set of headphones, but they are uncomfortable and dont appear to be made as well as the other headphones on this list. Overall they sound great. The bass is almost non-existent, like the HD598. The overall sound signature was not as clean as the MDR-V6. The MDR-V6 is just so clean and precise, very hard to beat. But the SR80i are still great headphones and I would probably prefer to listen to music and game with them more than the Sony's. The Grado's sound like what you are used to, which is not studio monitor headphones.
Now the Sennheiser HD598. I have the least experience with these, but they are so good I dont need extensive experience.
1. They are extremely comfortable. Even more comfortable than the MDR-V6 which is known for being comfortable. I find myself forgetting they are on. Some might say, "Well if you cant tell they are on, then maybe they are on too loose and will fall off." Not true. They are designed so well that they fit on snugly and have no pressure points.
2. They are open air which is a pro and a con, depending on what you want. You can hear most sounds in the environment with these on. The HFI-780 and MDR-V6 do a great job of blocking out noise. However, the open air nature of the HD598 gives better soundstage (you can hear where instruments are; in gaming you can hear where the bullets and the enemy are coming from; it sounds 3D) and better air venting. Your ears are the least likely to sweat with these on compared to all the other headphones listed.
3. They sound phenomenal. Of course there are better headphones out there, but for the $200-$300 price range, these are the headphones to beat. A respected audiophile says these are the best cans under $400-$500. The best way I can describe the sound is "smooth and creamy". One of the best ways to understand this is listening to a song where tons of instruments and vocals are going on. One example that I've used while comparing headphones is Mumford & Sons- Sigh No More. Skip to 2:23 and it starts getting complicated and intense. Many headphones cave under this stress, but the HD598 runs right through it with no resistance. It sounds awesome. In comparing the microscopic definition and exacting reproduction of sounds between the HD598 and the MDR-V6, the MDR-V6 takes the edge. But again, I still prefer the HD598 because it sounds better. With the HD598 you can still here the strings being strung, the reverberations of the instruments being used, etc. Although the MDR-V6 reproduces it more accurately, it also reproduces it more flat boring. Again, this is a fundamental difference between studio headphones (MDR-V6) and regular, fun headphones (HD598).
1. The bass is lacking. I'm not the listener who loves bass and eagerly tries to blow his eardrums at every possible occasion, but I do enjoy some thump. Bass is an essential part of music, without it, sound would be boring. I would say the HD598 gives you just enough bass to satisfy you. Using an equalizer or bass boost does help and does make a big difference. Open air headphones are notorious for their minimal bass reproduction. The bass that is produced sounds great though.
2. The cord, the cord!!! Although detachable, which is a pro, the con is that it terminates into the larger 1/4 plug (which can be a pro for others). I use the 3.5mm plug 99% of the time. The HD598 comes with a 3.5mm adapter turning the terminal end of the cord into a 5 inch plug section. When plugged into a Zune, iPod, etc, it looks ridiculous. Laughably ridiculous actually. I emailed Sennheiser about this and they said that will not make a cord that terminates into a 3.5mm plug for this headphone. Really unfortunate.
So when all things are said and done, after comparing the HD598 against several other well known and popular headphones, the HD598 are my favorite. They are not perfect. The bass is too soft, the sonic clarity is not quite as defined as the MDR-V6 (HD598 just slightly less, you can still hear ALL the detail), and the cord is ridiculous. But these cons are very very minor. The excellent sound and extreme comfort of these headphones, all things considered, are better than anything I've listened to.