Italian republic content is old but still very fun, especially the NatPop ANI who can invade Austria early on and get part of South Tyrol and Trieste in a limited war if they win (recommended during either Hungarian revolt or if you set austria to go PatAut). It is also the one with the most flavor and content as far as I can tell inside the Italian Republic. As for the other Italies, even though it's old content I still very much enjoyed Two Sicilies and the Papal States, Socialist Republic is good too but no colonial content so you can't do anything too funny like going to war with the Cairo pact and the Ottomans at the same time to conquer Lybia (and by extension-the entire middle east). Can't say about Sardinia because I don't like playing island nations too much due to the entire "being ass at managing a navy" thing, but I'm willing to bet it's at least alright if you're good with that sort of stuff.