For me, music is often the lesser of two evils compared to the background noise of the open office or the noise of the conversation going on in my own head. It also gives me a happiness fix which helps me not burn out and distract myself in other ways.
For me, it really depends on my mood and what I'm working on which type of music is appropriate. Some days it's rap and the flood of words doesn't get in the way even. Other days it has to be instrumental bluegrass or similar.