Venice
Venice's location was the absolute best position to trade with the East. Not only that, but as early as 1000 CE, Venice already had a strong economy from carrying goods by ship between Europe and the Byzantine Empire. It's population was a mix, from European Christians to those who practiced Islam. All their ideas and influence helped to kick start the Renaissance.
Florence
Florence was centered around finance and the trade of woolen cloth. It's tradition was to be ruled by a democracy. The city was ruled by a series of strong families, the most famous being the DE Medici family, who founded the bank and were known for wealth and power and the support of the arts.
Milan
Milan was formed into one of the most powerful and wealthy city-states from being ruled by the Visconti and Sforza family. The city of Milan conquered most of northern Italy from being so strong. One of the rulers in 1480 CE, Lodovico il Moro, supported Leonardo DA Vinci and the arts for almost 20 years. Not only that, but he created ambitious plans for canals and irrigation which encouraged farmers to grow new and different crops.
Rome
Naples
Rome was the central city of the Papal States. The territory was mostly controlled by the Pope and the Roman Catholic Church. It was the center for artists and scholars, and because of that there wasn't much trade or major industries, so they had to rely on religious and church business for financial gains.
Naples was mostly focused on agriculture. The man who conquered Naples, Alfonso, supported building, the arts, and education. Not only that, but he also founded a university for Greek Studies.