If you aren't an audiophile I wouldn't matter much about accurate sound reproduction, but I can vouch for Sennheiser. I had HD555's for a few years now and I still love them. I mix/master music, and they're decent at replicating sound for the price.
You can upgrade the HD555's to HD595's (a higher and more expensive model) by taking them apart and removing a piece of plastic which makes them sound worse than the 595s since its basically the same headphone minus these plastic strips (Dirty Sennheiser)
Even though the sound quality is awesome from Sennheiser, out of the TWO pairs I've had, TWO of them have broken, but it was easily fixed as I still had warranty on them.
Beats by Dre is overpriced, just like any other Monster product, but if you want to look cool/trendy and don't mind paying for inaccurate sound (overemphasized bass), go with them. I've listened to them, and my Sennheiser HD555 is close to and if not better than the Beats By Dre, and I got mine for like $99 USD.
It also depends if you are planning to walk around with them, or just keep them at home, because the Sennheisers I mentioned are strictly for a home/studio environment and you'd look like a tool wearing them in public, they have an MP3 player range which I haven't had experience with but check out the link below.
Sennheiser Headphone Range
As you can see there's something for everybody and I can definitely vouch for the sound. If you don't trust me just Google up reviews
