Best sci-fi system to start with

>>53902820
That entirely depends on what you want the system to be capable of and what you want to do.

Stars Without Number is an OSR sci-fi game, so it should fit in with your 5e experiences (as long as you don't expect 10 classes and archetypes).

I heard it's getting a new edition with improved rules, but it's entirely servicable as it is.

apologize in advance, new to this: as in like, a universe, like firefly, or star wars?

>>53902820
Never played it, but I hear traveller is the absolute go-to in terms of generic Scifi. From what little I've seen it's not terribly complex, and yet covers everything you need except maybe Psionics/Space magic.

Also FFG Star Wars is decent if you're fine with using an app/website/conversion table or just buy the special dice.

The games are about as complex as DnD 5e, the only thing that might come up difficult at first is interpreting threat/advantage & Triumph/Despair symbols, but after getting used to it it's especially fun with creative players. Also it takes a bit to get used from the DM side as you're not setting DCs but instead hand out difficulty dice that make a check harder to pass.
You might wanna houserule vehicle/space combat though, that's sadly the most janky part of the whole game.

Edge of the Empire especially can be used for a lot of generic Scifi if you refluff it. Age of Rebellion is a bit more married to the universe, but not impossible to refluff and Force and Destiny only works if you're willing to have Not!-Jedi Space Wizards.

>>53903516
Forgot to add: AoR and FaD are still fine as supplements, as all the non-jedi content like races, pre-statted enemies/ncs and some equipment and verhicle stats are backwards compatible.
Even if you don't want to carbon copy the alien races, taking ideas for possible traits and how they are used in the rules are always nice to have. Human Only is of course always an option too.

>>53902820
Damn, I think you spoiled your group with 5e, it'll be difficult to switch to an old system.

>>53902820
Refluff your weapons and armor.
Change currency from gold standard to credit standard with 1 copper = 1 credit.
And presto, it's done.

Far easier than forcing your players to relearn another new system if they don't want to.

If they do want to, then the latest Star Wars and Savage Worlds are both good and simple sci-fi system that able to do most popular sci-fi settings easily.

>>53903565
How's and why's that?

>>53903759
Because he's a grognard or he believes 5th to be a real smooth ride compared to primitive games that came before it.

On suggestions... it depends what you are after.

>>53903565
What the fuck are you even on about.

>>53903599
Dear god no.

>>53902820
Previous system shouldn't matter as any half decent system will always have good paragraphs on what playing the system is about and advice for the GM on how to run things the way the system intends. Science fiction is a pretty broad genre, what kind of setting exactly are you looking for? Space Opera, cyberpunk, Star Trek, Star Wars, what?

>>53902820
Players who have been playing 5e for a while should be ready to graduate to Pathfinder, and the upcoming Starfinder is Pathfinder in space so I'd suggest waiting for that.

>>53903864
>graduate

You mean downgrade to unplayable garbage?

>>53903864
You went full retard. Never go full retard.

>>53902820

What kind of sci fi? Space opera? Cyberpunk? Hard sci fi? A lot depends on what setting you use and how hard your science.

All the recommendations here are fine (except Pathfinder). If you're using a boxed setting like Traveller or Shadowrun, then the system that comes with it is fine. Hell, Rogue Trader's mechanics aren't great but should be perfectly playable.

If you're looking for hard sci fi, then it's pretty much GURPS. It's designed to let you do hard or soft, but most systems don't give you guidelines for running hard sci fi at all. Whereas GURPS supplements are excellent for that.

Transhuman Space in particular is a fantastic setting, hard as a rock but fun and incredibly imaginative and playable. It's written for 3e (99% of the complaints you hear about GURPS apply only to this edition) but the cheap and thorough supplement Changing Times is a conversion guide and playing THS in 4e is easy.

Do yourself a favor and grab the THS core book, just to read it. It's absolutely mind-blowing even if you never run it, or run it with some other game system.

Other GURPS sci fi settings. Reign of Steel is a post-apocalyptic "robots annihilated humanity" world. After the End is a more generic post-apocalyptic game framework. It just started coming out in PDF. Infinite Worlds is the parallel universe game, both a game in its own right and kind of a metasetting that lets you cross any game over with any other if the DM wants. Technomancer is a what-if world where magic was discovered in the 1940s and so it's both modern and high magic.

GURPS cyberpunk is pretty old now... but was written by a genuine OG hacker and so good that the US Secret Service raided sjgames and tried to shut the book down, calling it a manual for cybercrime.

Finally, and getting back off GURPS, check out this site: http://www.projectrho.com/public_html/rocket/

It's a definitive resource for building your own sci fi setting.

>>53904116
GURPS isn't the only choice for hard sci-fi. There's Orbital 2100 for Traveller, and Diaspora for FATE.

If you're interested some guy spent years making a halo rpg, it's called Halo Mythic and is free on the Halo Mythic reddit page.
I've only run one campaign with it that was a one and done (also my first time dming) which was decent, my players as UNSC soldiers