They are nearly identical
The tags are the same except 9=-1 and 6=+2 (instead of +1). There is a mild improvement in the Insurance Correlation of the Hi-Opt II.
I use the Hi-Opt II myself, but I don't think it would be more difficult to learn the AOII. My only concern was that it is difficult for a beginner to pick up a level 2 system with an ace side count. Since I assumed that Nina was a beginner looking for a good system I thought I should mention that it can be a bit tough.
If you are moving up from a level 1 system, I think that both systems are excellent. I might also advise the Zen system since it avoids the side count. That makes it much simpler for playing shoe games. It captures almost all of the betting power and the same Insurance Correlation of AOII.
Any system will become second nature to you once you get enough practice, so if you are dedicated enough I highly recommend these 3 systems. Just my opinions.
-Sonny-