Don't forget to call your bank and tell them you will be using your ATM card overseas, otherwise they'll block it thinking of fraudulent use.
It is a good policy, if you travel alone, to have two ATM cards from different banks, in case one is blocked, damaged or lost.
If you are traveling with someone make sure that each has a separate ATM card, so that you can cover each other in case one ATM card is blocked, damaged, or lost.
Only the most expensive hotels and restaurants accept AmEx in Italy. So I use Visa/MC, however my wife has AmEx and she carries it, since AmEx offers good travel benefits (like insurance) and gets you cash in case you are in an emergency situation with no cash.
Don't worry about locating ATMs. Italy has the highest concentration of bank branches in the European Union, to the chagrin of the European Central Bank, the bank regulator, who continually chastises the Italian bank system for having too many branches. There are more ATMs in Italy than in a Las Vegas casino, Any town with over 1000 souls will have at least one bank branch and a postal office, which in Italy is now a partly privatized large publicly held corporation which offers bank services, insurance services, and is even a mobile phone provider.