Which flavor headphones to pick?

Q: I'm looking at Beyerdynamic DT770 headphones, but they come in three flavors -- 32 ohm, 80 ohms and 250 ohms. Which one do I buy?

A: 32 ohm versions are easiest to drive, no amp needed.

80 ohm DT770s will be driven by many mp3 players and phones, but some devices with weak outputs may struggle, and if you amp a 80ohm DT770 Pro you will see modest sound improvement (tighter bass, for example, but this also is related to damping factor and the output impedance of the device powering the headphones).

The 250 ohm DT770 will definitely require amping. Some Beyerdynamic models have 600 ohms of impedance, and those certainly will need an amp as well to shine.