tar(1) has been around since the early days of UNIX , while afio(1) is newer and not installed on every system. The advantage of afio(1) is that it is smarter about corrupted archives, so if you have a read error somewhere in your backup, it will still continue and recover as many files as possible, while tar(1) would just abort. Further on afio(1) does compression file by file which is highly recommended for reasons of safety. The default format is AFIO.