Ok, here you can check the results so far:
link

With 110 votes, goggers currently decided that:
SMAC>Civ4>2>3>5>1>Coloniz>(rest)

They are all not bad. The first ones lack in graphics quality and user interface compared to current standards and the latter ones are too much streamlined. The peak was probably Civ IV and SMAX was just the best overall. The spin-offs, excluding SMAX, are the worst of it. However, Civ 1-6 can be recommended without hesitation.

I didn't play Civ VI yet, hope I can do it this year.

From the official "Civ" games, I like Civ 3 the most, but I probably like the "Call to Power" Series more because of their interesting game mechanics(public works, oceanic cities)

I suspect that a lot of people have not played it, and it requires some tinkering if you want to get it to run on a modern system. Plus, it's not available online, unlike Civ3 and later.

Personally, I'm very fond of Civ II, but I don't know if I would say it's the best game in the series. It's relaxing to play, and quite simple (plus, the lack of animations make it one of the faster games in the series to play), but it also feels a bit bare-bones.
And Alpha Centauri is more fun anyway ;)

Yeah, I really liked Civ1, 2 and 3 and SMAC. But I voted IV, VI and Colonization.

The older ones are classic but I wouldn't install them anymore. Even IV I'm borderline if to revisit it... and I skipped V but I think I'd also like it if I had gotten into it.

That's actually the only one of the first 3 I couldn't get into so much. What was it about it for you?
I have the original Civ 2 and it runs fine on my 32 bit Win7, not even sure if I set the compatability mode or not.

I kind of like the simple nature of 2. But I haven't played beyond it so I don't know which version I would prefer.

Oh and for the guy who said Civ 2 made Civ great, it was more glossy and more complex but it wasn't that much of a change from the original.

I played Civ 1 before 2 came out and it was a truly great game, the best I'd ever played.

What I like especially about the open source web freeciv version is that they have a 3D rendered planet view and that you can watch others playing. I think that Civ is a very attractive multiplayer system and a bit undiscovered so far in this regard. I hope this comes more in the future.

Now if someone would bring SMAX to the web and add an easygoing multiplayer matchmaking and everything.

Oh, now SMAC and Civ4 are tied.
And finally Civ6 got 1 vote lol.

I have only played around with 2 and 3 (and Alpha Centauri), and I prefer 2 to 3 because 2 has a *much better* cheat mode. In Civ 2's cheat mode, you can do things like editing cities (changing their size to something not reasonable, like 0 for example), destroy entire civilizations, and switch the game into 0-player mode. Civilization 3's equivalent is severely limited by comparison, which was rather disappointing.

In any case, since it's an option I think I would go with Alpha Centauri because it has a cheat mode similar to Civilization 2's (though it's called the Scenario Editor, I believe) and it allows you to create custom units (like a unit that can fly and has the Settler's "build city" ability). Psionics are also an interesting equalizing mechanic, though it is disappointing how late you get the ability to give that capability to your own units.

Edit: I voted for Civ 2, Alpha Centauri, and None.

Civilization 1 because it started it all, after that SMAC.

Obviously, the "None" option should be voted alone, you cheater :P
(the poll site doesn't have too many advanced features)

The only one I've played to any extent is V, so I can't really give a valid comparison.

I did enjoy the old, original Colonization when I played it back in the stone ages.

It requires a 3rd party video codec if you want the videos. I don't know how well it works in a 64 bit OS (which really is the norm these days), but I should give it a try one of these days.

Original Colonization was my favourite, having played that, Civ 1-5 (including 4's Colonization), Alpha Centauri (which a kindly gogger provided trying to get me into it) and FreeCiv and FreeCol.
Just something about it that none of the others captured. Could very well just be nostalgia, of course.

The second one, because of the whole nostalgia thing and because it was a present from my father.

Otherwise, I just go with the most recent one. I could play any one of them and enjoy it, but usually just stick with the new kid on the block.