I would really think it would be hard to break M50's, they are built solid. They have survived dropping, ran over with computer chair. I have a large head, so I have to really stretch them out (bend them). I used the box they came with overnight and they are super comfy. I needed a closed phone because I work in a quiet environment.
Bass, well I have to be honest I only tried the Sony's at Best Buy and they didn't work at all for me. Could have been the crappy player they had them on. Like I said, the source is 90% of it. The biggest jump in quality came from a decent $100 sound card rather than the crappy onboard sound chip.
A lot of people around here don't believe in EQing, amping to add bass, but I think it just sounds awesome. I know that the M50's have a V shaped sound, but that is really what I wanted. The M50's just make the music sound crystal clear to me. I have had plenty of muddy phones, and wanted to get away from them.
When I got my first pair of M50's they were about $110. Now, they are they are $160, like the HFi 580 that DVDRey mentions. Honestly, the HFi 580 and M50's probably are both quality phones. You get what you pay for, well most the time that is true unless you buy Bose or Beats phones... How many times do you see a headphone go UP in price over a year or two?