I voted for 1.9.1.
Savegame incompatibilities have always been part of the TripleA development during the last 8 years…
As long as you can run different TripleA versions side by side this is not really an issue.
So just finish your ongoing games with the version installed - and start new games with the new version installed next to the old one. No wizardry.
The major issue when changing from 1.809 to 1.9 has been the map incompatibilities - due to the rewrite of the maps themselves on the one side and the change of the map install directories on the other side. As this definitely won’t repeat when proceeding from 1.9 to 1.91 - there is no reason not to go on this way.
We want to improve TripleA - we want it to be as rules compliant as possible - we want it to be as flexible for adding house rules or creating different games as possible - so we need to accept savegame incompatibilities from time to time.
The more improvements and bug fixes are added to the engine the more this is justified, of course.
I am happy to give support to everyone who wants or needs it here in the software forum - as always. :-)