I agree, Playing Sardinia-Piedmont is a very good way to have fun as a beginner. Just want for the 50s for the alliances of the other italian states to expire and you can conquer Lucca, Parma and Modena in a couple of days. Selling France's core provinces helps having enough cash to last long enough to unify Italy (try to keep the coal-producing one though).
Once You form Italy, you should become a Great Power in no time and have plenty of core provinces to acquire in Austria, so the game stays interesting. You can also try with Two Sicilies, but it's slightly harder.
As for the nations who definitely deserve to be tried, CSA has to be played through the CW, but I guess it's not as good for beginners.