[Rama Set]

I choose the united federation of planets circa season 3 of TNG.

Why specifically?

The UFP is presented as a sort of perfectly efficient Union of socialism and democracy. Everyone has their needs fulfilled and can do what their heart desires. They are economically prosperous and culturally prolific. Their conflict almost exclusively originates from without and their judicial system is geared towards rehabilitation and is quite successful at that. It is basically a socio-political love fest.

[Yaakov ben Avraham]

It would be possible to create a general intelligence AI that could function similarly to a 'benevolent dictator' but we still end up with the question of how to go about doing that.

G-d help us if the AI ever malfunctioned though. Then we'd all be f----d, and at the mercy of a malfunctioning supercomputer.

[Ghost Spaghetti]

The ideal state is one which satisfies the material  and psychological needs of its people, is flexible enough to alter itself to changing needs, and is governed with the support of the majority and the consent of all.

I don't think such a state exists or has ever existed, but ingredients for an ideal state would be a high quality of education, low levels of financial and legal inequality, stable and reliable infrastructure, freedom of thought and expression, including a safety net to support people who cannot support themselves.

[Lord Dave]

The ideal state for me is one where everyone in it agrees with me and the government runs itself in a way that I approve of.
The form of government is irrelevant.