Hmm. That is a good question. Finally.
My favorite game that has actually stayed with me - we'll get back to this in a bit - has to be the Star Wars RPG by West End Games, commonly referred to as Star Wars D6.
There are a lot of reasons this game has stuck with me, with the prevailing one being it is just really good.; it is a exceptionally well put together game with consistently good supplements and decent auxiliary products that works just as well today as it did in the 80s.
The system is the closest I've seen to hitting that perfect sweet spot between rules lite and detail, fluff and crunch, with only Free League's ALIEN RPG giving it a run for its money. Not only is it mechanically sound, it is mechanically comfortable for me to the point where I can run it without the rulebook for the most part. Not long ago, after a long time of not playing it, I executed the rules for taking multiple actions incorrectly but after a quite check things were back on track. Not that I know and remember how that rule functions, well, I once again don't need the book.
It is also very much Star Wars and not just Star Wars, but a particular flavor of Star Wars that I really love. It's 'Original Recipe' so to speak. The game feels like the Original Trilogy because that's what it was made to emulate and all we really had to go on back then.
Star Wars, The Role Playing Game just punches in all the right coordinates for the perfect jump to lightspeed. If you have tried it, give it a go.
May The Force Be With You,