I GM Swords and Wizardry. It's sort of a combination of AD&D and white box D&D. (There are assassins but no half orcs.) The rules PDF is free if you'd like to have a look. There's a lot of support material if you like that sort of thing (adventures, setting books, etc.)So, assuming you folks do OSR AD&D, why? What’s your path and POV?
So I started running it for a few reasons. The group I was GMing (in 5e) would regularly let the rules get in the way of their fun. We also started playing on a VTT, which was slowing down the gameplay. Then also, I wanted to start writing a big OSR adventure for publication, and they were interested in playtesting.
What initially interested me in OSR was Pathfinder. It just became too rules heavy for my taste. I tried in vain to get my group (back then) into Castles & Crusades, but they were "Pathfinder for Life" (in fact some of them are only now considering 5e).
But where am I with the OSR now? I'm running two 5e games, one PF2 game, and playing in an Old School Essentials game. I'll go back to OSR when everyone is ready.
There's not a "best system" to me. It depends on what the group wants at the time.