Audio-Technica ATH-M50 or Sennheiser HD555 headphones?

I'm planning on buying either one of these two headphones. Which one do you think is better and why? What's better about one than the other? I am by no means an audiophile really, but I do enjoy high quality equipment all around. I'll be using them primarily only listening to music on my PC, but maybe sometimes I might hook them up and watch TV with them as well, possibly even use them for gaming, but I have a Turtle Beach headset for that. Oh, and I will also lug them around to listen to my iPod with as well.