I've been raving about the MrSpeakers Mad Dogs since I got them last week and the more I listen to them, the more I am convinced these are real giant killers.
At around 250 to 265 dollars, The Mad Dogs are better at accurately reproducing music than nearly every high end, 500 dollar and up headphone I have personally used (and I have used a lot of them). There are no nasty treble peaks like the high end Grados and bass extends much farther without rolling off. There is no exaggerated bass hump like the Denon D5000. There is no grain to the sound and there is more clarity than the HD600. The bass is less rounded and the soundstage has clearer depth and precision than the HD650.
Plus they have technicalities to match up with some of the best headphones out there. They are very fast, they have amazing pinpoint imaging, they have a layered 3D soundstage, There is no unnatural ringing or resonances producing harsh treble or a shouty midrange. The bass is pretty flat and extends below 60 Hz. It's well behaved and not wooly or dirty bass. There is no graininess to the sound. it's smooth and clean.
I have never experienced a headphone that cost so much less than the competition that actually sounded better than them. Not just "pretty good for the price". That's what has amazed me about these.
Their weak points compared to the TOTL headphones I have heard. HP1000, HD800, LCD3, SR-007.
They do not have the same bass extension as the LCD3. they're pretty flat down low but there's just more bass power with the LCD3.
They do not have the same tall and wide soundstage as the cans I just listed (except the HP1000). It's precise and layered, but not huge.
They lack a bit of sweetness in the midrange that you get with the LCD3 or the SR-007. mids are a tiny bit drier.
They're not as neutral in FR as the HP1000 or SR-007. but they're still pretty darn good. I find them to be flatter than the HD800 as there's no treble peak.
Another weak point, at least compared to something like a Grado PS500, is that they truly require a pretty powerful amp to drive them. So finding a good portable amp might be a challenge. I'm currently using an ALO Continental at work and Burson Soloist at the desk for them. I'm curious to try an O2 in the future to see if something more affordable can drive them as well as I am hearing them now.