Caro Rubenm
reading between the lines I guess you would really enjoy a mixture of country and city, and the freedom of the car.
This suggests that my very home town, Rome, would possibly not be a good choice, for a number of reasons:
1) it is not a car friendly city but above all
2) just to get a first impression of Rome would require the full allowance of your 4 days.
Using it as a starting point only would not do justice to the city.To be honest I lived and there for 26 years and did not manage to see half of it!
So, better to leave this destination for another car free trip. Having said that, the area on the south side of Rome is very beautiful especially around the vulcanic lakes of Albano and Nemi, an area known as the Castelli, of wine fame. But as I said, I would be reluctant to recommend Rome for your kind of trip.
I think landing in Turin and exploring the surrouning area is probably a very good choice. Unfortunately I don't know this region personally but I know it has the right character and pace for what seem to be your style. Turin itself is an elegant town, formal capital of the kingdom of Savoy an then Italy. A visit to the town will possibly demand a day of your time. From Turin I suggest you visit the following places:
Saluzzo, a very beautiful medieval town:
http://en.wikipedia.org/wiki/Saluzzo
Alba, famous for its towers and truffles. This is South of Turin. It sits in the middle of an interesting rural area called Le Langhe. Find information on this town on:
http://en.wikipedia.org/wiki/Alba_(CN)
You may also wish to squeeze in a visit to the North, either to Aosta
http://en.wikipedia.org/wiki/Aosta
or to the Grand Paradiso Alpine area [a national park] see
http://en.wikipedia.org/wiki/Gran_Paradiso
If you prefer to land in Milan, you will find this city more congested than Turin and more practical than pretty, with the exception of some notable tourist sites such as the renaissance church of Santa Maria delle Grazie (with the famous Leonardo's last supper fresco - you need to book in advance to visit this), the medieval St Ambrogio Church as well as the renown Cathedral square, Piazza del Duomo and adjacent Galleria- a turn of the century shopping centre of the highest spec!.
There are many beautiful towns accessible from Milan. I would suggest the following:
Pavia as seen on
http://en.wikipedia.org/wiki/Pavia and Mantova
http://en.wikipedia.org/wiki/Mantova with its stunning location surrouned by waters. Both are to the West of Milan and within easy reach. Lastly I think Bergamo could be to your liking, the original town of Arlequin, see
http://en.wikipedia.org/wiki/Bergamo ,this time to the North of Milan and on the slopes of the Alps.
I hope you have a great trip. Don't forget to tell us about it!
roma55