ATM,
Barbarians only (my vote). I like the idea, the problems it has are now fairly minor and I don't feel that it has any detrimental aspect - it just fits in nicely in any game.
C&M could be such a mode, but sadly the AI luxury improvement issue ruins it. As long as it unfixed, I will only start game with it to further produce save reproducing the problem - or if I want increase my chances on purpose to win on high levels...
Secret Societies is another close one. I see myself now enabling it in most games, though I probably don't want to have the infusion of extra goodies in any game. Another minor aspect is still the AI - Cultist use has improved, but it is still probably not a mode making the AI more of a competitor.
Tech Shuffle is great addition I don't want to miss as option, but I just don't want it in every game - so this is the perfect case of an occasional use mode for me.
DA is thematically great, but the implementation is too rough and extreme for my taste for permanent enabling; also it greatly hits the AI. I see myself enabling it from time to time, if I really want to have drama in my games - but surely not always.
The rest ist just not my cup of tea (
Apokalypse, Zombies) or the absent AI (
Heroes) is preventing me from trying it at all - and the question I'm faced with when it comes to playing those modes, is whether I will
ever do so. Apokalypse and Zombies are least likely (just don't like the concept/gameplay); Heroes are borderline. I could probably accept the fantasy in some games and would like to explore the features attached to the heroes...but the AI not using them is unfortunately a complete showstopper, IMO.
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Is it like with me and SS? I like the mode so much I don't care, Voidsingers are utterly broken AI wise?
I think it is combination of the AI problem here only hitting roughly 1/4 of your opponents (and even those have received at least a slight fix in one of the last patches) and even then, it just doesn't feel as serious as with C&M. Sure those AIs will sink some faith in useless Cultist purchasing/squandering, but it doesn't completely lock them out of the competition.
So, yes I'm also surprised how popular C&M is in its current shape.