So we of course have to begin by acknowledging that wealth comparisons are incredibly difficult in the context of ancient and renaissance economies is next to impossible. Instead I'll present to "snapshots" of cities in Italy to explain how vastly different they were economically, and then present my hypothesis at the end.

Cities in Roman Italy: I'm going to assume you're referring the height of Imperial Rome, so what did urban centres look like economically at this time? As maligned as Malthusian concepts of capacity might be, they do apply to Roman Italy, simply because the empire allowed for a scale of grain export to Italy that dwarfed anything that occurred until the modern era. As a result, Roman cities, especially Rome, where far larger than they "should have been". Additionally, Roman dominance over the Mediterranean allowed for the first real emergence of "economies of scale" in the Mediterranean. This meant that it was often cheaper to import goods than to produce them domestically. Not only were major cities usually "awash" with goods from across the empire, but so were smaller inland market towns, a clear sign that it was cheaper to import pottery from a part of the empire where it was mass produced than manufacture it domestically. So what does this mean? Roman cities, especially those in Italy were large, well-connected to trade routes, generally contained large scale manufacturing, and were almost entirely monetised.

Cities in Renaissance Italy: Likely smaller than their Roman era antecedents, but well-connected to trade routes and at least in terms of the larger ones, highly if not completely monetised. Many of these cities also had large-scale manufacturing, but unlike their Roman counterparts, these industries were generally labour and capital intensive enough to necessitate a high degree of investment. This is however, where it becomes difficult to make a direct comparison. For example, Milan was well known for its weapons and armour, and Venice was well known amongst other things for its glass work. The difference here is that in Ancient Roman cities wide-scale manufacturing came about due to economies of scale, while in Renaissance Italy if often came about due to the capital intensive nature of their selected manufactures. Now, with regards to the trade routes these cities were connected to, they may have been "richer" in the context of their focus on prohibitively expensive luxury goods from the Silk Road, though at a far smaller scale than Roman trade, which was focused more so on the movement of Mediterranean goods (grain, pottery, oil, wine), with a much smaller focus on textiles and spices from without.

My conclusion: probably Roman cities. Why? Roman cities were larger, better connected to trade routes, and crucially, united under a single polity. Ancient Rome had a rate of internal migration that could have reached as high as 40%. Major British market towns could have had, for example, Greek tutors, Phoenician merchants, and Gaulish craftsmen, all of whom had moved there for the purpose of making an income. Membership in a single polity also meant that everyone spoke Latin, if not as a first language than as a lingua franca, and had the same laws around trade, which was hugely important for long-distance trade. For example, in the early Medieval period, Jewish merchants were so successful because Hebrew served as common language that a Yemenite Jewish merchant and an Italian Jewish merchant both knew, and could thus conduct their business more easily together than merchants without any common languages. Membership in a single polity also meant a lack of duties and custom payments. Additionally, the Roman economy operated on such a scale, that excavations of ice cores in Greenland have shown that Roman lead mining produced 20% of the air pollution that modern-day industrial lead mining does.

TLDR: Roman cities were larger, better connected to trade on a higher scale, and politically unified with the rest of the Mediterranean Basin. Hope this helps!

Edit: For an example of the scale or Roman industry, look up the Barbegal Mill Complex by Arles. Its one of the largest extant ruins of a Roman manufacturing complex.