Anyone (yes, anyone) who attempts to advance the idea of eradicating monogamy is flirting with madness.
I'm certainly not suggesting to eradicate monogamy and replace it with these, and it wouldn't make sense to say any one of these is holistically better than the others, but if we're focusing on just the "what's best for kids" angle... wouldn't it be better if kids had _more_ parents/very close adult relatives? More people in their life they can rely on for attention, advice, care, etc.?
Even in this super-rare case where one father lives with multiple wives, the attention/resources of the father is still divided among even more children. Also, the wives usually view the other children as competitors. The dynamics of this setup are known from old harems/courts.
Or Infidelity...