It's been a few years since I tried alternatives, but I ended up back at MS active directory. AD is one of the things Microsoft did really well, and supported forever. It's a shame they're working on killing it off now.
Everything else kinda worked for the most part, but there would always be issues I'd have to work around. That might have gotten better over the years, but I wouldn't count on it.
What do you mean MS is killing off AD? As far as I know they’ve just renamed Azure AD. (But there’s a good possibility I’ve missed something.)
MS AD - well it just works and if you're looking to learn for industry experience it's the one to go for. Spin up a Windows Server trial edition, re-arm the trial every 180 days and have it running for nearly 3 years. Just before the trial expires completely you migrate the domain to a new install and continue on for another 3 years.
Running Samba-AD. It has it's issues and can be painful but seem stable enough.
Never gotten in to FreeIPA. If you're needing Windows authentication, it's not the one for you.