If I were teaching people I would use a plain 2-digit Major System (or the 2-digit system I use). Enthusiastic students could expand that to a 3-digit Major System or Ben System.
PAO requires three times as many images than a simple 2-digit Major System, and it might not provide that many advantages – see the death of PAO for a discussion about it. (It doesn’t mean that PAO is dead – just that it is less-represented at the very highest level of competition as it used to be.)