I have found that whatever peace blocking noise gives you, it is more than offset by the paranoia of being watched or the terror of people sneaking up behind you.
For me visual distractions (even if it is just people walking) are a lot worse than noise. I can tune out the chatter but whenever I feel or see movement around me, my head snaps to attention to find out what it is. Some evolutionary thing most likely
I have had this happen to me a few times. Really into my work with my ear phones & music playing, can hear nothing besides my music. Turn to the side and my co-worker is there waiting on me to go over something. Scares the *$#$ at of me every time.
FWIW, I've seen some people attach a small convex mirror to the edge of their monitor to avoid this kind of surprise. I'd expect this is just trading audio distractions for visual ones, though.
Unless you fly or are muting HVAC or server room sounds, I haven't found that noise-cancelling headphones are superior to isolating (close-backed circumaurals or in-ear monitors). NC doesn't work well for voices, and the extra expense tends to put them into "I'm too paranoid to keep them on my desk" category.
I'd save the $$$ and just go for a nice pair of isolating ones.
I've also become a huge fan of wireless headphones for the added mobility--I switch between a few different computers and monitors, and not wrapping myself up in the wire is worth a slight hit in the sound.
Sony MDR-10RBTs are an excellent model for the price, hella light and comfortable, don't leak much sound out or in, and sound quite decent with Bluetooth AAC/AptX enabled (I listen to rock, metal, industrial, pop, dance, rap--can't speak much for classical, jazz, etc.)
