I like large galaxies that I edit to slow the expansion of the AI's. Gives a more realistic feel to the game. (220 systems) give or take.
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Creator of the Star Trek Mod - AST Mod - 78 Ship Sets - Conquest Mod - Atrocities Star Wars Mod - Galaxy Reborn Mod - and Subterfuge Mod.
I prefer the following - high tech cost - me against 3 or 4 AI players - in 255 system galaxy that i edit myself - put in at least 40 planets in each system - reduce the black hole - nebula systems etc maybe to 1 per 100 systems. - ive made mines tech cheaper (and limit my minefields - the AI puts out limited amounts) - made missile weapons more expensive (they are to much of an advantage early on) - beam weapons are slightly cheaper - ive created more mineral tech levels and changed the facility amounts
And the same with radioactives and organics - as well as research and intel facitilies - it makes for a longer game - makes it more difficult expansion wise at the beginning - ive made lots of other small changes ie 25 ship tech levels with ship size ranging from 100 kt up to 10000 kt per ship
10 levels of base 300kt - 20000 kt - makes for some interesting battles
Cargo facilities go up to 10 levels with 8000 storage.
Numerous other adaptations for my "special" mod and im still tinkering.
On the standard 1.91 game though as MM has it - well 255 systems with 5 AIs at most.
High tech cost doesn't hinder the AI any more than it hinders you. In fact, it probably helps to stop the AI from retrofitting its ships every few turns. Also note that in a SP game with an AI bonus - it'll be even more difficult for you to keep up in terms of tech making it more of a challenge.