In a competitive sense, the Audio Technicas sell for $10 more but have the advantage of a substantial studio heritage and better word-of-mouth. But apart from a slightly better build the Brainwavz have several other things going for them. The Brainwavz headphones are more sensitive than the ATH-M50s, meaning that they can output more volume and sound good for mobile use, and they're more neutral, too.
I used the Brainwavz as my main set of work headphones for several weeks and found this neutrality to be suited to most music, but they do sacrifice some dynamics compared with the punchier ATH-M50s. Whether it was the delicate strum of acoustic guitars in pastoral R.E.M. tracks or the full-blown mental breakdown of Future of the Left, the HM5s were always excellent communicators. About the only people who would be disappointed by these lovely sounding cans would be dubstep fans.
While the ATH-M50s have a warmer, "rockier" sound than the Brainwavz with a fuller bass response and more treble sizzle, the Brainwavz offer better clarity and a wider soundstage. Additionally, the HM5 has a very open sound, which is very hard to achieve with a closed headphone design. By contrast, another headphone -- the more costly AKG K551 -- attempted this but forwent bass response for more "air" and resultingly could become screechy with the wrong music.Conclusion
Which headphones should you go for: the Brainwavz or the Audio-Technicas? Both are good at different things. If you want something that will render your music and media in a dynamic way, then choose the ATH-M50s, but if you want something more neutral and comfortable, choose the Brainwavz.
As an aside, the Brainwavz are reputedly identical -- according to Head-Fi users -- to the Lindy HF-100 and the Jaycar Pro Monitor Headphones. While we can't vouch for this, they all do appear to be sourced from Taiwanese company Yoga, and at even cheaper prices than the Brainwavz version, how can you go wrong with either?