When in Rome (and other Italian cities), Uber or a white taxi?
First things first, Italy remains a fairly regulated market when it comes to transport. Cabs (white and clearly marked) are still the pre-eminent form of non-public transit. They're numerous, available and charge metered rates (with various supplements). Rome Uber is the new kid on the block, which means it still flies mostly under administrative radar. Uber rates are generally higher than cab rates but there's wiggle room, depending on driver and route. The Italian app works pretty much like its American counterpart and English is (mostly) spoken. So far, so good.
Realistically speaking, however, cab travel still remains your best bet. It's quicker, cheaper, and drivers (generally) know what they're doing and rarely cheat (yes, of course, there are bad apples). A cab is still what you want if you're stuck someplace in the city and want to get home. They're still Italy's chicken soup, so to speak. Most companies now have their own apps, led by 3570, Rome's largest cab coop.
Cab drivers don't have the overhead of Uber cars, often upscale, gas-hungry Mercedes. They also don't pretend to give you a boutique experience. They're hackers in the old sense.
Deregulation may yet come to Italy, putting Uber rides, rates and availability — more to the point, accountability — on par with cabs, but we're not there yet. For now, if you're a stranger in a strange land, take a white cab, whether at the airport of from your hotel.
Let Uber and its ilk flourish in deregulated markets where they've all but replaced cabs, in particular the U.S.