Warlord.
I used to play Civ 2 at Deity level all the time, and almost always scored 250 to 350 percent. One day, for a break from the intensity of trying to do well at Deity, I played a couple of games at Monarch to Warlord levels. Like the "Sultan Bhargash" above, I thought it would be go back and mop up.
And found that it wasn't really that different. Just less frustration from population being "born" unhappy at the higher levels, as the biggest difference. It also seemed like the AI at Monarch was a more skilled opponent than at Deity. <shrug>
It also seemed as if the scoring system was biased slightly in favor of higher difficulty levels. Looking at the various scores submitted for games of the month, I think that's probably still true in Civ 3. In other words, it's impossible or nearly so to get a really kickin' score at Warlord, but not as impossible at Deity.
Having long since proven my point to myself that I could play and consistently beat Deity level, I didn't really feel like I had anything to prove anymore. I settled comfortably into Warlord level, because it has the least frustration from unhappy population. My life already has more than enough sources of frustration; no need to seek more from the games I play. Most of the pleasure I get from playing Civ is the model-railroad type. I sometimes even played at Chieftain, depending on whether I wanted an opponent AI that was more crippled or felt like being able to see certain game information only visible at Chieftain, or wanted to be able to switch a city from producing one thing to another without losing half the shields accumulated so far, etc.
So, now I play Civ 3 at Warlord level. Some day I'll take a shot at Monarch or so, just to see if it recaptures those first few games I played at Monarch and Deity with Civ 2. There was a real high that came from hanging on in those games and surviving, and then getting good enough to clobber those games. But I'm not sure there's a lot of learning curve in doing the same thing with Civ 3 that would interest me at all. Most (not all) of that learning curve I've already figured out with Civ 2 or Warlord-level Civ 3.
I'm an old-school wargamer, by today's standards. Cut my teeth on Avalon Hill and Tractics, followed by SPI. So not a _true_ grognard by standards I grew up with. True grognards would be those who were veteran gamers before the publication of Tactics II, meaning that they were limited to miniatures gaming and no board games. Much less RPGs, lol. Anyway, I'm originally more a wargamer than model railroader, so when it's time for my little Civ empire to grab some resources from another empire or retaliate against aggression, I still enjoy getting all adversarial against the AI instead of being content with merely pruning my garden all day.
I turn off all victory types besides diplomatic and conquest. I don't really want my game to tell me when I'm done playing for score. I should be the one to decide that. I paid my $40 and want my money's worth, dangit.
-freaked