Purely for audio listening, air conduction is the better option since good sound quality, volume, and a certain degree of noise isolation is maintained. Sound tends to get leaked from bone conduction devices due to its open design, so audio quality and noise isolation are compromised. However, if you tend to use earphones/headphones for long periods of time, bone conduction might be the better option as they can help prevent ear damage and pain. It is also best suited for people with certain kinds of hearing impairments.