[Edi]

As far as I know, the AI decision making is the same regardless of level, but the amount of bonus or handicap varies. The lowest level of AI gets a -25% handicap on gold, iron and special resources and is named Piss Boy. The highest level of AI gets a 500% bonus and is ranked Emperor.

Scarcity or abundance of resources is the main determining factor in CoE3 on whether you will prosper or not. Start locations are random and you can get really lucky or unlucky with them, so playing against AI that gets some bonuses is advisable. The default AI gets a 25% bonus, but I make a point of playing against AIs that get 50% or more bonuses.

The reason being that the AI can't always factor in everything when picking its fights, which can lead to really lopsided results sometimes. Also, more resources allows the AI to garrison its citadels. IF you lose all citadels, you're eliminated, so that's kind of important.