Age of Merchants is probably the best all around. Because it is:
A) Beautiful (visually)
B) Clear with good visibility
C) Complex and difficult
D) Asymmetric
E)
Perfectly balanced, which is extremely rare amongst difficult maps. (For example, I really like
Pearl Harbor, but must admit that it is not well balanced)
It has a few flaws, though. It is not very suitable for 1-1 games (but MOST maps isn't!), because initial drop could be extremely generous, especially if a player plays first. Also, it is too slow in 6p no cards games (but again - MOST maps are)...
However, 4p no cards on this map is perhaps the best game you can make on CC.
I never played
World 2.0, but it's obvious that this map is very good. It is:
A) Ugly, but this feature has a lowest priority amongst the mentioned.
B) Visibility is far from excellent, but acceptable
C) By far the most complex of all classical maps. It is even comparable with difficult, non-classical maps - due to enormous number of countries and continents.
D/E) Asymmetric and (I'm convinced) well balanced
A flow is that it demands many players. Even 6 players is not enough (starting bonus is to big for my taste).
However, 8p flat rate on this map is probably one of the best games you can make on CC.
Age of Magic is:
A) Almost as beautiful as Age of Merchants
B) Clearness and visibility are at least acceptable, although 6 and 5 neutrals look almost the same
C) Seemingly simple, but actually difficult
D/E) Asymmetric and seemingly (I played only one game and lost on purpose, to free a slot) very well balanced. If DiM confirms to me that he has a strategy against nearest neighbor who plays before you, plays aggressively and has a hell of a good dice - I'll vote for this map as the best

...
Very good for 2p and 3p games. Also, in 6p no card games is not slow as on other maps...
Virtually every game on this map is good.
And of course I must vote for
Clasic. It's not a very big map - only 42 countries. But it is complex enough and very asymmetric. I ADORE huge distances which you can't find of other maps of similar size...