And as a secondary question, with which conditions you think the game is most balanced?
IMO, 250-400 stars with occasional colonies is the best setting, because it means the game won´t end too fast, while allowing for each ship to feel useful and unique, instead of the massive spam that happens in larger games. Sure, microing escorts and frigates is a bit too much, but I want at least to setup my main fleets and control them. Also, it means colony management (and conquest) and technological choices will be more critical.
As for races and governments, both technocracies and mercantile guilds make the game quite easy, and quameno/zenox + technocracy makes the game a cakewalk. It´s way too easy to get the wonder Shipyards and colonization tech and expand waaaaaay before everyone else.