1. Dungeons and Dragons (AD&D 1e, BECMI/RC, Some AD&D 2.5e and 5e) being what I've always played. If I were to run an old school D&D game, I'd probably use RC D&D combined with the Labyrinth Lord and other compatible OSR books I have. I still play in an AD&D campaign I joined in '86, which makes 1e the RPG I have played the most. 5e I enjoy because it's elegant and versatile. Sure it's different from old school D&D but it feels pretty darn close. First game I ran using 5e was set in Karameikos.
2. Cortex Plus Heroic particularly Marvel Heroic coupled with the Hacker's Guide and skills from Firefly. Use Time Dice in place of Initiative and you have the fastest combat resolution for play by post games I have ever seen. This is my go to system for running games on forums. I borrowed and adapted the Approaches from Fate Accelerated and used them in place of Affiliations. Since Approaches are verbs which can easily become adverbs, I also swap out Specialties for Firefly Skills which are verbs, and can be combined to form sentences like, "I ly the with my ". This let a player not only declare what they were going to to but it also let them build their dice pool right from the sentence. When Cam gets licencing sorted I may be very happy.
3. d20 Star Wars Revised Core Rules is the most fun I have ever had running a d20 system. I infuriated my players, using dungeon dice to map out the ventilation system of an Imperial Star Destroyer, made a joke about how air ducts are always clean then chased them down with the droids that clean the air ducts. Good times. I know that Saga Edition is cleaner and easier to run, but at the time it didn't exist. I liberally borrowed from d20 Modern/Future and I did horrid things like send them to Planet Ravenloft in one adventure and Planet Granbretan in another. When a certain player got all canony at me, I'd pull out the 3.5e Monster Manual. They did not appreciate my swapping out Quarren for Mind Flayers. I liked 3.5e but I liked this d20 game a lot more.
4. Mutants and Masterminds 2e/True20 A long time ago, there were forums for the True20 game which I got into because I thought Blue Rose was neat. I liked True 20 more, and I also liked Mutants and Masterminds since 2001. A fellow on those forums named Shadow took True20 and applied it to the Mutants and Masterminds point system used in 2e. The two games were pretty close in any case. You could pull the Vampire from the True20 Bestiary and it was really close to the one in the M+M rulebook. Other creatures in both books had similar stats which let me say "good enough" and use the Bestiary wholesale in M+M. I do like Mutants and Masterminds 3e and have probably played more of it than 2e, but as a GM the 2e/True20 mashup was really fun for Pulp/Street level mystery horror games.
5. Pinning down a 5th is hard. It could be Doctor Who Adventures in Time and Space, or FASA Star Trek or Aliens (Phoenix Command Lite) or Battletech/Mechwarrior or Marvel Superheroes. I'm surprised I got to number four to be honest.

Quote from: Celestial;756656My five favorite RPGs would be BASH!, Buck Rogers XXVC, DC Heroes / Blood of Heroes, ICONS, and Shadowrun.

Granted I very much doubt I'll ever play Buck Rogers XXVC nor DC Heroes again, but those two games will always have a special place in my heart.

I really enjoyed the Buck Rogers XXVc RPG. I used it in combination with 1e Battlesystem so I could do fleet vs fleet battles. Some good times there. I read all the novels too and I still have most of them. I really like the idea of a solar system centric game, and I've used that setting in a Mutants and Masterminds 3e game.

Five Favorite RPG's

1 Mine
2 Torg
3 Shadowrun 2nd ed
4 D&D 3e
5 Savage Worlds
6 GURPS 3e supplements / Rifts (tie)

Tough, but lemme see...

1.) Street Fighter: The Storytelling Game - It feels like modern adventure and the fighting system is enjoyable.
2.) The Fantasy Trip - Deceptively deep and clever with its magic and being built as a combat/vs. game, it feels solid there as well. Has some odd game-ness, but I can live with it.
3.) ACKS (to choose a D&D) - Keeps many of the benefits of Basic D&D, but with tools to add complexity if you want.  I do prefer turns, combat phase and "initiative by side" in my D&D though.
4.) Runequest 6/Mythras? - Kinda dry, but satisfyingly emulative. Tools to build the kind of world you want are nice.
5.) Castle Falkenstein? Heavy Gear 2nd ed.? (I don't know what goes in #5) - I can't decide. It could even be something other than the 2 games listed as contenders. They both have charm, though.

Here are my picks, I've played each game in the top five at least once, usually more. The Honorable Mentions are a mix of games I have played and games I find interesting and have read.

1. Big Eyes Small Mouth First Edition/The Sailor Moon Role-Playing Game and Resource Book
2. Advanced Dungeons & Dragons (Both 1E and 2E)
3. Vampire: The Masquerade First Edition
4. Street Fighter: The Storytelling Game
5. Mage: The Ascension Second Edition

Honorable Mentions: Original Dungeons & Dragons, Werewolf: The Apocalypse 1E and 2E, Vampire: The Requiem 1E, Changeling: The Lost 1E, Pathfinder, GURPS 3E, D&D 5E, D&D 3.5, BESM D20, Only War, HERO System 5e Sidekick, Recon, Black Tokyo

I have to answer this in two parts:

SYSTEMS

I.FASERIP
II. Cineflex
III. Runequest 6th Ed
IV. Star Wars (WEG)
V. Outlaws of the Water Margin

SETTINGS

I. Warhammer Fantasy Role-play 1st Edition
II. Paranoia
III. Planescape
IV. Changeling: The Dreaming
V. Shadowrun 2nd Edition

AD&D 1st ed/Moldvay D&D and to be honest, all modern OSR retro-clones
Call of Cthulhu
d6 Star Wars
Hackmaster 4E
Marvel Super Heroes (FACERIP system)

In no particular order:  L5R, D&D, specifically ACKS, and Traveller ... and that's it for the top rank, really.  I like Savage Worlds well enough, but I don't go looking to play a SW game for the rule set so much as I may get enthused about a setting.  And I have fond memories of Rolemaster, but it's not a system I'm trying to get back into.

These are the games that I've had the most fun with, they're not the best, nor will I ever say that they are 'good', just that I had a blast, or found them most useful.  And I am not ranking them, despite numbering them.

1. Mutants and Masterminds (all editions, but mostly 3rd now)
2. FFG's Star Wars Edge of Empire
3. Feng Shui (both editions)
4. Palladium's Rifts
5. Runeslayer (A Runequest game that was never officially published)

These are the ones I've had the most fun with, but there's about thirty or so I've had fun with as well, not to mention that I'm willing to try anything at least once.

1) Lejendary Adventure
2) AD&D 1st Edition
3) Dangerous Journeys
4) Dark Conspiracy
5) WEG Star Wars

We revisiting our posts? Cool.

Quote from: Ratman_tf;8380091. 2nd Edition Advanced Dungeons and Dragons

Still a solid #1. I sucessfully broke in my house rules a while ago, and things ran smoothy. I prefer 2nd to 3rd, but did change AC and THACO to be ascending.
I also made the proficiencies ascending versus difficulty number, and rolled the thief abilities into the proficiency system. Worked great, and rogue types actually have a chance at using their abilities at low levels now.

Quote2. Cyberpunk 2020

I'm going to bump CP2020, and give credit where credit is due.
Rifts.
The Palladium system is like a broken down jalopy, but the world is crazy fun, and I do enjoy tinkering with that old jalopy. Gets the #2 spot because we played a ton of Rifts.

Quote3. Earthdawn 1st Edition

A solid #3. One of my best campaigns was run in Earthdawn, and I'd love to get a chance to GM it again.

Quote4. Dungeon Crawl Classics

I love DCC, but I'm going to put Mekton 2nd edition here. Interlock is a solid system, and I used Mekton for a ton of mecha games. Even kitbashed it for a Wing Commander campaign.

Quote5. Stars Without Number

Can stay at #5. The few times I've gotten to run it, the system is great. I feel it just needs the right published setting to catapult it up into a higher slot.

My top five:

1.  D&D Red Box, first played in 1977, the game that started it all
2.  AD&D (1st Edition)
3.  Star Frontiers
4.  Twilight 2000
5.  Villains & Vigilantes

Yeah I know those are all old school.  Honorable mentions:  Call of Cthulhu, Swordbearer, Bushido

As for what I'm playing now:  REH's Conan RPG (2D20 Modiphius); MYFAROG

1. Basic Roleplaying
2. Artesia
3. The One Ring
4. Houses of the Blooded
5. Rolemaster (with lots of house rules)

Honorable mentions that I played, but never ran: GURPS, FATE
Pendragon looks fantastic in theory, but I never tried it