The best type of government is natural...

It's the one already inside of us: Federal Republic

All of your organs are autonomous but act under the brain
It's a healthy mix of centralization and decentralization.

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Also it wouldn't be a Confederacy because that would imply voluntary unification.
While true that it was a voluntary unification, it's not true that it would be voluntary for states to leave the Union once in during the first American Confederacy. If you read the Articles of Confederation, it says somewhere that the Union shall be perpetual; that hasn't changed since the current constitution came into effect.