My favorite level to play is Emperor. I also find it more challenging than Deity for reasons explained below. But it looks to me that most players consider Deity the most challenging. The following comment is one of many examples:
My reason for preferring Emperor is that I feel Deity skews the game too far in the direction of managing happiness. Surely managing happiness is one of the important aspects of this game but there should be a balance among the various aspects and I feel that balance is better in Emperor vs. Deity. Another reason I dislike Deity is all the micro management I have to do at the early part of the game to make sure my cities stay out of unrest. I can do it, but it is not much fun. The game requires too much micro management as is.
Finally, here is my reason for believing that Emperor is actually more challenging than Deity. First let us see what the trade off is. In Deity you get one fewer content citizen compared to what you get in Emperor. But you get two settlers to start with regardless of your starting position. As far as I know everything else is the same. I do not know, and I suppose nobody else does either, whether the AI is any smarter in Deity vs. Emperor. But I have played enough to instinctively believe that there is no difference. Assuming that I am right and the only difference is one fewer content citizen then I think that Emperor is more challenging because:
1. A None settler is far more valuable than an extra content citizen at the beginning of the game when most of my cities spend most of their time in size 1 anyways.
2. As time goes on, in the great majority of games, we build enough cities to get to black head citizens. These guys are much easier to make happy than the red heads and in Deity you get them sooner.
So except for a short period of time when my cities are larger than size 1 but I still do not have enough cities to see black heads, Deity is tougher to play; before and long after Emperor is.
Some Apolyton players studied ... at Diety level, but maybe later at other levels (Apolytoners seem to feel other levels were beneath them! so other levels weren't studied so much).
My reason for preferring Emperor is that I feel Deity skews the game too far in the direction of managing happiness. Surely managing happiness is one of the important aspects of this game but there should be a balance among the various aspects and I feel that balance is better in Emperor vs. Deity. Another reason I dislike Deity is all the micro management I have to do at the early part of the game to make sure my cities stay out of unrest. I can do it, but it is not much fun. The game requires too much micro management as is.
Finally, here is my reason for believing that Emperor is actually more challenging than Deity. First let us see what the trade off is. In Deity you get one fewer content citizen compared to what you get in Emperor. But you get two settlers to start with regardless of your starting position. As far as I know everything else is the same. I do not know, and I suppose nobody else does either, whether the AI is any smarter in Deity vs. Emperor. But I have played enough to instinctively believe that there is no difference. Assuming that I am right and the only difference is one fewer content citizen then I think that Emperor is more challenging because:
1. A None settler is far more valuable than an extra content citizen at the beginning of the game when most of my cities spend most of their time in size 1 anyways.
2. As time goes on, in the great majority of games, we build enough cities to get to black head citizens. These guys are much easier to make happy than the red heads and in Deity you get them sooner.
So except for a short period of time when my cities are larger than size 1 but I still do not have enough cities to see black heads, Deity is tougher to play; before and long after Emperor is.