Probably the most reliable opinion I've found so far is at Headfonia. They seem to think that more "cheaper" headphones is better than one "good" one:
"Rule #3: More Headphones Is Better Than One Headphone
What I’m saying here is that it’s better to own three $100 headphones than one $300 headphone. Or three $300 headphones than one $900 headphone. Why? Because most people don’t limit their playlist to strictly one genre. And following the logic from Rule #2, the right headphone-music pairing is going to be better than one expensive headphone paired to the wrong music.
This is why headphones are so fun. It’s easy to switch from one pair to the next. Imagine if you were listening to speakers, you would need three different rooms to set up your three different speaker sets."