For this point 2K Games was quite vague as to what the next-gen version of the Standard Edition will really bring to the table as exclusive features, the attributes used to warrant the higher price point. So far we know MT NBA 2K21 will receive the loading display rate new gameplay features, some gameplay modes, and that next-gen hardware will deliver.
We do not have confirmation how a lot of these changes will be accessible for the current-gen variant of the Standard Edition, which is playable on next-gen consoles via backward compatibility. Less than two months out from current-gen release, this is a small puzzle that lovers are having to fix. At minimum this is an inelegant scenario compared to how other significant sports developers are handling these problems, like EA offering Dual Entitlement for Madden 21 and FIFA 21 at no extra price.
For players that just can not wait the couple of months NBA 2K21 will probably be outside on current-gen consoles before its next-gen introduction, the current-gen Standard Edition will likely be well worth it. If you think of the $60 as a time investment, and compare it to something like the cost of a movie theater trip (inadvisable during quarantine, mind you), then you are likely able to average out the value to around $5 per amusement hour. For players who will play 12 or more hours NBA 2K21 before next-gen release, something we expect many players to do in their very first sitting, this is going to be a worthy buy.
The question for these types of players is if the Mamba Forever Edition is subsequently worth the additional price to avoid having to buy the two versions of the Standard Edition, something that would cost $130 rather than the $100 for your Mamba Forever Edition. At the end of the afternoon, players who appreciate the excess couple months NBA 2K21 will be just playable on current-gen consoles and also hope to play NBA 2K21 more than this time period will come across the Mamba Forever Edition that the best value in the long term.
This is especially true for gamers who invest more time on their MyTEAM compared to MyPLAYER and MyLEAGUE, as MyTEAM is the only mode that Buy NBA 2K21 MT will carry over advancement from current to next-gen. This doesn't take into account the additional bonuses that come from the Mamba Forever Edition. For players that don't meet these standards, based on preference, picking up version of the Standard Edition will be the right choice. Although the next-gen version will probably be preferable due to the enhanced exclusive features.