Portable music players don't offer optimal audio quality anyway, so the difference between a pair of $150.00 Bose headphones and $7.00 Sony headphones isn't EXTREMELY EXTREMELY different.
I personally think that people who wear headphones look weird with them on. Freaking huge, thick pieces of ugly plastic wrapped around the ear.
I only wear my headphones at home, sound quality matters, but outside people who wear it look like faggots.
Earbuds look sleek and they're way better for transportation and running. When I run, wearing think headphones that pool up in my sweat isn't so cool.
Most headphones break easily anyway, and it's hard to put them away. It's quite cumbersome to me to have to wear my headphones around my neck the whole day.
Plus many headphones "leak" sound to the air around it. So a group of rappers might hear you listening to Bjork and start laughing at you, even if you don't mean to leak the sound out.
It's personal preference, but I prefer wearing earbuds outside. There's many factors that make up for its poor sound quality and discomfort.