As far as "My favourite Civ game", I'd be hard-pressed to choose between AC and Coloni
sation[1].
So Col had less starting-nation choices (the major European Powers) than either Civ (Americans to Zulus[2]) or AC, and it was Civ1-level graphics[3] compared to AC's fine isometric(+) artwork, but rather than 'just' a bonus to horse unit/free additional diplomat/whatever, the nation-advantages seemed more meaningful. And I've just reinfected myself with the earworm music by shear recollection alone.
AC impressed me, I think, by being Col-level factionally divergent, bonus/mallus-wise. More so than the graphics (though the overlaid "chassis+body" unit construction thing was a revelation to me at the time, I think; at least in terms of sprite-based graphics). It gave, notwithstanding my "'always' flood the world" half-memories, different ways to play the game, that didn't just give a slightly different initial impetus towards the inevitable pursuit of whatever's next in the Ironclad/Roailroad/Tank/Nukes list, whether personifying Gandhi or Ghengiz.
(English, under Col, were better for their colonist pool/training situation as you organically expand, Dutch for trading opportunities, Spanish of course promoted the warfare element. Definitely a vastly different game - at least until you eventually severed links to your home nation.)
I've not really touched the main Civ series post-3 (maybe VI?), so maybe I've missed out on that. I've got UnCiv on the Android tablet (from the comments in the Updates, it seems to be a cross-platform thing) that I presume echoes the latest 'true' Civ in the way many Open fan-recreations do (for XCom, Transport Tycoon, Elite, etc, but also with extra inbuilt modability) and it disappoints me with the non-stackability/-tile-sharability of allied units which seems like a retrograde step forced on the game by programmatical concerns. And there seems no way
not to annoy the AI nations (move units towards their territory they dislike you; fortify units/build cities across their approach and wait for them to discover you and they also dislike you; expand away from your founding city in the opposite direction and they encounter your capital first... they dislike you). Yes, there's an appeasement/paying-off mechanism, but either it's broken or I am.
Or it may just be that I've gone past the basic plasticity of my brain that I had three or four decades ago and, goshdarnit!, why are they messing with things that used to work! (Things that were themselves tweaks of things that worked well enough, but at the time I appreciated the jump from Doom to DoomII far more than I felt the advantage of what came after - Duke Nukem 3D excepted, the shrill sound of the subway train squeal background atmospheric effect also now coming to mind
alongside the colonial piping of Col...)
[1] An 's' because I'd often be the English (at least at first), goddamnit!
[2] Ironically, my two favourite starting nations on Earth-map. Zulus if I could quickly get a unit up to blockade the block that was badically Suez before any other nation got into Africa by land, the USof Americans something similar but with Panama or thereabouts, so I didn't immediately have the Aztecs to worry about (just Barbarians).
[3] Being on the DF fora here with me, I know you'll all appreciate that a game can be primitive-looking but not primitive-playing!