What is the best space 4X game you guys can recommend me?

Galactic Civilizations: I personally have the Ultimate 2 and it is good, but VERY complex!
Civilization 5: A beast, and easy to pick up!

I've also heard good things from Sin of a Solar Empire, but can't give you feedback on those (the Trinity version is in my wishlist)...

I'm sure there are others, but those are the ones I personally know.

Homeworld 2

Upcoming Galactic Civilization III looks decent but costs ridiculous money on steam. Check also X series, Master of Orion too, but only if you don't mind ancient games.

Best ever was Alpha Centauri: Alien Crossfire, but it's extremely dated now. Can still get it on GOG though.
Endless Space is pretty fun, but it's very shallow. All the parts are there, but no soul.
Sins of a Solar Empire's pretty neat, but don't be fooled by screen shots of pretty graphics. 90% of your gameplay will be watching static mono-colored icons slowly moving around. You CAN zoom in, but any time watching the fireworks is time not managing your empire (and it's real time).
Civilization V is ok, but I feel it lost something from the earlier Civs. No real impact on the land is possible, the in-game help for units/races/buildings is lacking, stats aren't well exposed, and the system optimizations never been good, but with a couple buddys it's your best bet for world conquest fun.
I do love Galactic Civilization II, but the lack of multiplayer's pretty glaring. GalCiv III promises to remedy that.
If you find a better game right now, I'd love to hear it. Otherwise, I'm waiting on GalCiv III, Endless Legend, and Beyond Earth.

I have Endless Space and played a few games. It's a good indie 4X game and I had fun with it. My only gripe with the game is that it felt small. Even with the largest galaxy, I didn't have to go far to bump into the AI. While I liked the time I spent with the game, I felt that there were better 4X games out there.

So, I installed Sins of a Solar Empire and Civ 5. I plan on giving them both a go and see which one I like better.

Well, obviously Civ 5 and Civ 4 are two of the best 4X games ever made. If you're looking for space 4X, Gal Civ II is probably the way to go. That's the only one that has managed to suck me in for hours-long play sessions. Endless Space and Sins of a Solar Empire are both good games with nice-looking ships (something Gal Civ lacks), and they have a newer feel than Gal Civ II, but Gal Civ II is more of a Civilization in space type of 4X, which I like.

Galactic Civilizations

Cant forget stardrive, I believe the creator is working on a new one

The "Best" 4X game I think should be split into different categories.. Such as Space 4x, Historical 4X, Fantasy 4X...

my personal opinion X3: terran conflict and albion prelude are still among the best out

classic x4 games I would say is MOO2 and Space Empires IV. Not sure if you are interested in old games. Star Ruler is one of my personal favorite. Currently playing Armada 2526 Gold edition, can't say I'd recommend that game.

I read comments, I have played Gal Civ 2...I do recommend that game. Endless Space is ok...I love everything but research (too much of +% this and +% that) and combat mechanisms.

Civ 5 Complete Edition is on my wishlist, I only have the base game...it looks good. I recommend that game to try out.

The most fun I've ever had with those type of games was with a game called Escape Velocity: Ev Nova

You can download a free trial there from their website at no charge. 30 bucks is a bit steep for a game of it's age, but you can download the mods for the first 2 games in the series to run on the engine so its like paying 10 bucks per game.

Eclipse, though it's a tabletop or iOS game.

Endless Space!!!

Someone else already mentioned Master Of Orion 2 here, I'd like to recommend that also. I've been hoping that someone would make a game that was as good as it in the space 4x genre but nobody has yet. It's simple to gasp with a fantastically well designed UI yet complex enough to make it a game you always want to come back to. I would strongly recommend this game to anyone who is thinking about trying the 4X genre for the first time. Sadly this game isn't on Steam but you can pick it up at GoG, its bundled with the first one for 6 bucks. Definitely worth it for such a fantastic game. Also MoO 1 is very good if you don't mind the graphics.

As a side this is a game I've been following and I'm looking forward to seeing how it plays when it comes out: clicky

Galactic Civilizations 2 Ultimate Edition. No contest imho.

Aurora, nicknamed the dwarf fortress of space.

No, it has no graphics, yes, it's the best one, and by far.

MOO2:BAA is still the gold standard, despite it's dated features and obvious flaws. I think I've bought it at least 5 times since it was released... put hundreds of hours in it via LAN play in my dorm during my college years, too.

I tried Endless Space and I really liked it. I gave GalCiv 1 and 2 to a buddy and he was really digging it, but I haven't had a chance to try it yet.

As an aside: Steer clear of Master of Orion 3. Like, if anyone ever recommends the game punch that person in the face--it's unlikely you'll receive a criminal record if you explain why to the judge and the judge has ever played it.

Space Engineers

Master of Orion 2 :)

Warlock - Master of the Arcane or Endless Legend

Why isn't Sins of a Solar Empire suggested 500 times!!?!??

MOO2. No need to go any further.

Well Freelancer ofc.

Master of Orion 2 - it's been very influental on everything that came after and I still prefer it over any others