So, I can give a quick breakdown, but it's impossible to give a full feature comparison as that would involve in-depth knowledge of all four's respective development.

Let's start, oddly, with vindicta.
Vindicta was created by several members of an older Antistasi dev team who split off to create their own rebellion game mode as Antistasi didn't work for them as a base. Beyond this it is not related to Antistasi directly.

Now for the different Antistasi mods:

Antistasi Community:
The current official community development.
Endorsed by the original creator Barbolani, and developed for over 4 or 5 years, this is the most current of the following three as far as the mods go.

Antistasi Plus:
A mod of community, created by Socrates to address some mechanics or gameplay changes he wanted to see that weren't covered by the community version or it's development direction. I believe it is no longer maintained, but I could be wrong.

Antistasi Ultimate:
A mod of Antistasi Plus that further added and changed mechanics based on another development teams vision, contains further mechanics and mission types, some QoL things for players.


Hope this helps a bit for which is which, but for a full idea of what's different I'm afraid you would have to start looking at changelogs, and there's quite a lot of them across 3 different Antistasis.

TL;DR:
Vindicta is a completely different game mode, but made by an old Antistasi team.

Antistasi Community is official and most frequently updated.

Antistasi Plus is a mod of community by a solo dev.

Antistasi Ultimate is a mod of plus by a small team.

Thanks for the run down.

Aside from Vindicta, which Antistasi version between Community and Ultimate would be more single player friendly?

I play Community as solo. Haven't tried the others.