It's CivIII for me. I take the opposite view as Breunor - CivIII seems very strategic to me while Civ4 doesn't seem to have nearly as much true strategy. Perhaps it's in the micromanagement.
CivIII by far takes the crown for the game that I've played most. I got Civ4 right away since CivIII was good, but it ran so poorly it just wasn't as fun. And I probably had my expectations set too high after CivIII. Oh well, live and learn, I won't be so quick to rush out and get Civ5.
And really, I like the graphics in CivIII as much as in Civ4. Although that was alleviated somewhat when I turned on Single Unit Graphics in Civ4 looking for a performance boost - instead I got much better looking battles. Civ4 does take points for having more tile improvements and having a regular grid. And it gets points for showing every building in a city - although CivIII's city view screen was in some ways better - mainly that you could see it all in one nice, big view without messing with zooms.
The smaller maps in Civ4 also pushes me towards CivIII. The average number of cities just isn't high enough in Civ4. Even with Monarchy or Republic you get more productive cities in CivIII on the same sized map as in Civ4, and with Communism it's no comparison.
I also kind of like being able to have "Communism". The civics is an improvement, but I kind of wish it were more of an edict system - if anyone's played the game Tropico, they'll know what I mean.
Religions are a nice addition at least in concept, but as they are now with no differences it's pretty bland. Governments wouldn't be much fun if they were all the same except for different names, either.
I like the idea of the new promotion system. And it is fun to get very skilled Legions, Redcoats, etc. But the CivIII combat system was also good, and I liked the Army unit a lot. Warlords did address this somewhat; alas I do not have it.
Civ4's combat system gets points for having unit v. unit differences (i.e. pikemen excel against horses). The only problem with this is that if there's pikemen and crossbowmen defending and you have macemen and knights, either way you're in for a really bad time.
I can't stand Civ4's artillery and airplane system, though. CivIII's artillery acted like real artillery would, bombarding stuff, not going on the offensive against horsemen like in Civ4. And city buildings aren't immune to airstrikes like in Civ4. I can see Wonders being immune so the game isn't unfun, but if a library is destroyed, just rebuild it.
I'm hoping Beyond the Sword makes Civ4 comparable to CivIII for me. It looks like a much better expansion pack that Warlords.
But Civ4 does have room for improvement with its structure. The editor isn't nearly as easy to use as CivIII's, and while unfortunate in that respect, I think Civ4 does have more overall mod-ability. If only there were a nice, simple XML guide to show you how to do the basic tweaks of CivIII's editor, Civ4's editing would be quite adequate.
CivIII by far takes the crown for the game that I've played most. I got Civ4 right away since CivIII was good, but it ran so poorly it just wasn't as fun. And I probably had my expectations set too high after CivIII. Oh well, live and learn, I won't be so quick to rush out and get Civ5.
And really, I like the graphics in CivIII as much as in Civ4. Although that was alleviated somewhat when I turned on Single Unit Graphics in Civ4 looking for a performance boost - instead I got much better looking battles. Civ4 does take points for having more tile improvements and having a regular grid. And it gets points for showing every building in a city - although CivIII's city view screen was in some ways better - mainly that you could see it all in one nice, big view without messing with zooms.
The smaller maps in Civ4 also pushes me towards CivIII. The average number of cities just isn't high enough in Civ4. Even with Monarchy or Republic you get more productive cities in CivIII on the same sized map as in Civ4, and with Communism it's no comparison.
I also kind of like being able to have "Communism". The civics is an improvement, but I kind of wish it were more of an edict system - if anyone's played the game Tropico, they'll know what I mean.
Religions are a nice addition at least in concept, but as they are now with no differences it's pretty bland. Governments wouldn't be much fun if they were all the same except for different names, either.
I like the idea of the new promotion system. And it is fun to get very skilled Legions, Redcoats, etc. But the CivIII combat system was also good, and I liked the Army unit a lot. Warlords did address this somewhat; alas I do not have it.
Civ4's combat system gets points for having unit v. unit differences (i.e. pikemen excel against horses). The only problem with this is that if there's pikemen and crossbowmen defending and you have macemen and knights, either way you're in for a really bad time.
I can't stand Civ4's artillery and airplane system, though. CivIII's artillery acted like real artillery would, bombarding stuff, not going on the offensive against horsemen like in Civ4. And city buildings aren't immune to airstrikes like in Civ4. I can see Wonders being immune so the game isn't unfun, but if a library is destroyed, just rebuild it.
I'm hoping Beyond the Sword makes Civ4 comparable to CivIII for me. It looks like a much better expansion pack that Warlords.
But Civ4 does have room for improvement with its structure. The editor isn't nearly as easy to use as CivIII's, and while unfortunate in that respect, I think Civ4 does have more overall mod-ability. If only there were a nice, simple XML guide to show you how to do the basic tweaks of CivIII's editor, Civ4's editing would be quite adequate.
In civ IV you simply can't put that much of cities without cripling your empire and/or the computer 
Besides that and the animated advisors ( I loved the diplo one 
