I would assume NextGen includes AU accounts. Back when it was developed, FICO had not started cracking down on AU accounts. However, I do not know for sure.
All FICO models are different. When I think of NextGen, the first thing that comes to mind is NextGen wants to see a mix of bank/cu credit cards and store credit cards. FICO 08 doesnt' care about store vs bank/CU cards. FICO 08 wants to see open installment and revolving credit history. FICO 04 doesn't penalize you for not having both open revolving installment and revolving credit history. On the other hand FICO 04 does penalize you if you only have credit union/local bank credit cards. It likes to see at least one national bank in your credit mix.
NextGen is on a different scale than most other FICO models. An 800 on NextGen isn't as good as an 800 on FICO 04.
I am assuming you have a lender that uses NextGen. If they provide your score for a denial or not best of terms, you should get reason codes as to why your score is not higher. That will probably be the best way to try to maximize your NextGen score. However, maximizing your NextGen score may not be the best for your other FICO scores. It can also damage other scores (e.g. Auto Insurance risk score).
PS. You can learn a good bit about each FICO model by looking at the possible reason codes. Here is an old thread:
http://ficoforums.myfico.com/t5/Understanding-FICO-Scoring/Complete-list-of-FICO-Reason-Codes/td-p/3...
