I am torn between 18Titans and RWBY.
Most of the other options have already been done in some form, so would be nice to see some RWBY, since the only other one I could find is someone making a vr game and not really a "dating sim" type of novel like this.
The main thing I really like about four elements trainer has been the fact that they really have been following the main story of the series with some changes for dramatic, comic or sexy reasons.
18 Titans already has the base so I suppose it would take less time since it does not really need the startup of other options, plus they style fits the characters.
Ben 10 games have been done and are fairly good (even if the main one right now has been uber slow updating)
Main problem the RWBY game could have is that it is on a series that is not finished, so it would either be original story or just start trying to follow the main story that we have with the mentioned changes in story to keep the flow of the game story. With the story the good thing is the game takes time so it could give the series plenty of time to end (since it does not seem like the series has much seasons left unless they have some more story to add to current or some unexpected twist) but that said there is a lot of time between seasons so the game could actually come to a halt if it reaches a point that the series has not yet been aired.