I have owned the following headphones (in order):
1. Beyerdynamic DT770 Pro 80 (still own, use for travel)
2. Thunderpants (woody T50RP mod)
3. Audeze LCD-XC
4. MrSpeakers Alpha Prime
5. MrSpeakers ETHER C
 
I feel each headphone was a step up from the one before it. Also note that except for the Beyers, all are planar magnetic designs. I have owned nothing but planar and planar hybrid speakers for around 30 years. There is just something about their sound that no dynamic driver can equal.
 
The Audeze were great 'phones, but their weight was literally causing me pain (I wear headphones several hours a day at work). Also, they didn't have the same voicing as the LCD-2, which I loved listening to at meets. I found that while resolution was great, they were too far off neutral.
 
I bought the Alpha Prime without having heard them. I knew I liked the T50RP mods from my Thunderpants experience. Deciding I liked them better than the LCD was immediate. More neutral, and there was fatigue I wasn't even fully aware of listening to the Audeze that was completely absent with the Alphas. ETHERs weren't under consideration as I need closed cans.
 
Much to my dismay, the ETHER C was introduced not long after. I talked with Dan, the owner, and he said they were better in all respects than the Alphas, so I got on the waiting list. When I got them, I have to agree. They have the same neutral voicing as the Alphas, but beat them in detail and imaging. I had to really hunt for a single minor con to list. I have not had a chance to A/B unfortunately with other flagship headphones I have heard, but going by my memory, I have never heard a better closed headphone, and with open cans, I would need to go with something like the Stax SR009 to have a chance of bettering the ETHERs, and the Stax are in a completely different price range, especially considering how much you have to spend on electronics to have them be their best.
 
The ETHER C is completely non-fatiguing, sounds great on all types of music (I listen primarily to rock, alternative, bluegrass and classical). They are comfortable, have good isolation, and are very attractive. I recommend the DUM cable, I was not able to better them with aftermarket. Dan is great, he participates in the forums, and is always looking for ways to better the product. Since the C was released, he sent free tuning pads out to all customers and also has offered to existing buyers new backing foam which improves sound at a small cost (haven't tried mine yet). he is very responsive to email.
 
Highest recommendation for this product.

Please see my full review here:
http://www.head-fi.org/forum/thread/539012/review-leckerton-audio-uha-6s-usb-toslink-dac-amp
 
I have rarely been so enthusiastic about any product as I am about this unit. I can't recommend it too highly. The brand deserves much more name recognition than it is getting. These should be on the short list for anyone looking for a portable amp.

[size=medium]Directly compared:[/size]
[size=medium]Sony MDR-7509HD (my last headphones)[/size]
[size=medium]Sure SRH840[/size]
[size=medium]Sennheiser HD380 Pro[/size]
[size=medium]Beyerdynamic DT770 Pro-80[/size]
[size=medium]Beyerdynamic DT880 Pro[/size] [size=medium]- Show quoted text -[/size]


 
Tonal accuracy is very good. I am using as a reference my home theater with Sunfire XT ribbon hybrids and Bag End professional mastering subwoofers. The all important mid-high region is spot on. Bass is slightly emphasized, true, but the degree is exaggerated IMO.
 
Transients are very good, bordering on excellent.
 
Imaging is very good, bordering on excellent. Bettered by semi-open and open headphones, but they have their own drawbacks.
 
Comfort is very good - one can adjust the spring tension to one's preference - very nice feature.
 
Isolation is Good to Very Good - a bit above mid-pack. I haven't seen a variation in this aspect amongst closed backs, excluding super high isolation special purpose cans.
 
Main drawback is load/efficiency. In my experience these can not be adequately be driven by either a laptop sound card or by an MP3 player, even the powerhouse Cowon D2. I have a Turtle Beach USB DAC/amp at work, and a Total Airhead for travel. Without amplification, sound suffers substantially.
 
Note that if you are listening to these without a few hundred hours use on the phones, you aren't getting the full sound quality. Over time, I found that the bass became less prominent, mids/highs smoother, and imaging improved substantially. These phones have one of the longest break-in periods of any audio product I have ever owned.
 
I can and do listen to these all day long at work and on the plane. Very non-fatiguing, highly recommended.