I hardly ever use vassalage, serfdom, and environmentalism. Not to say these civics aren't useful, just that I never really learned how to get the most out of them and my style isn't geared towards using them. With that said, if I am spiritual anything goes and all of this is irrelevant.
a) No Vassalage b/c in the early game when it becomes available bureau usually nets me more overall than the free unit bonus would (but I will use vassalage if the bureau bonus isn't worthwile) and I also prefer using theo if the extra XP is what I am after;
b) serfdom b/c I rely heavily on slavery and in the rare cases that I don't whip, it's caste system (until emancipation)
c) environmentalism b/c it's either SP or FM. The health bonus isn't useful unless I really am lacking in health resources, which is rare towards the end of the game when environmentalism becomes available. Ditto for the lack of forests. Also the extra corp costs make it inefficient if I am running sushi or other corps; in my games I am either really spread out and using SP or heavily spamming corps and raking in the dough, so enviro just gets lost in between.
a) No Vassalage b/c in the early game when it becomes available bureau usually nets me more overall than the free unit bonus would (but I will use vassalage if the bureau bonus isn't worthwile) and I also prefer using theo if the extra XP is what I am after;
b) serfdom b/c I rely heavily on slavery and in the rare cases that I don't whip, it's caste system (until emancipation)
c) environmentalism b/c it's either SP or FM. The health bonus isn't useful unless I really am lacking in health resources, which is rare towards the end of the game when environmentalism becomes available. Ditto for the lack of forests. Also the extra corp costs make it inefficient if I am running sushi or other corps; in my games I am either really spread out and using SP or heavily spamming corps and raking in the dough, so enviro just gets lost in between.