The Hobbes' argument in Leviathan calls that civil peace and social unity are best achieved by the stablishment of a commonwealth through social contract. On Cicero's argument the commonwealth is a constutition of the entire people, where they united due to the spirit of congregation which naturally belongs to humans.
In Leviatan, the commonwealth is ruled by a sovereign power responsible for protecting the security of itself and granted absolute authority to ensure the common defense. To Cicero's, the ideal ruler to a commonwealth are the People in all, to ensure the tie of social affection and the public interest, so it can mantains its force.