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.

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.)