This was my favorite thread on the old r/OSR. So is your favorite system/systems?
I'll start:
Basic Fantasy - BF gets overlooked a lot because the print books are sold at cost so I think it ends up being a lot of peoples introduction to OSR, but I keep coming back to it. The modules are really well written.
Old School Essentials - Just got the Rules Tome and I love it, though I haven't had the change to dig into a game with it yet.
Want Full-Knuckle Gonzo? Labyrinth Lord + the Advanced Edition Companion + Mutant Future + Apes Victorious + Starships & Spacemen.
Is it as pretty as OSE? Nope. But you can download Labyrinth Lord + the Advanced Edition Companion + Mutant Future without art for free. If you want art, you do have to pay. They all work with each other.
Hyperborea (Described to me as effective AD&D 1e but refined) is my first, so it's all I know. That said, I'm really enjoying pouring through it. My players for my Delta Green game are very excited to play too, but none of them have played OSR before either, so part of me worries they're in for a rough time with how deadly combat is.
Honestly not a bad choice. I remember when I was a kid, those books were already pretty old and were very cheap. (early 90s) I wish I had collected more of them.
Swords & Wizardrymy review of Revised - OD&D rather than B/X which is very cartoony. Much more, uh, complete than White Box, much simpler than AD&D, really a great sweet spot.
Advanced Fighting Fantasy, Troika!, etc. - great simple game, minimalist rules, setting-as-system in Troika's case.
Monsters! Monsters! is replacing Tunnels & Trolls, which has been bought & sold a couple times now and is in limbo. M!M! runs all the T&T adventures, esp. the solos, and is a great pick-up game.
I love the adventures for Lamentations of the Flame Princess, but the system's been neglected, the Referee book is still not out, there's no monster book, etc. But the adventures work in any OSR game with minor tweaking.
There is a monster book, but it's a book about generating monsters rather than using existing ones. This is a deliberate choice that's explicitly stated in the guidance Raggi gives to writers interested in submitting new content you can find posted... uh... somewhere.