1.12.1 I would e.g. Add to 1.12 for the sake of simplicity.
Gladly write something about it.
Logically, answering only makes sense if you have played / played it.
I don't play online that often, which is why I always find the newest version the nicest.
I've been playing minecraft for 6 years and actually only survival speedrun, so I prefer the latest version.
Pvp system is best at 1.8 in my opinion. However, when you play Survival I think the newest version is better as there's a lot of new stuff.
I think everything from 1.13 on is not that great for multiplayer, but I also don't think 1.8 because there are no observers.
I'm a Redstone player xD
It just depends on what you want to do. For a survival project or something, I would always use the latest version, because that's where most of the content is. But if you want to play PvP now, I would say that 1.8 is the best version (I know 1.7.10 was actually better for PvP but most servers no longer have support for it).