... traditional taxis in Vienna often scam passengers
This is not true. I have a long experience with taxis in Vienna, and never have had a bad experience. All officially licensed taxis in Vienna must charge the same fare by law. Do not bargain about the price, insist that the meter is on. (Certain routes, e.g. to/from the airport, are offered for a flat fee not only by taxis, but mostly limousine services [e.g. €30].) All taxis bear a license plate ending with TX, whereas limousine services have MW.
Usually you do not pick up a taxi on the street. You call it by phone (+43140100) or walk to a taxi stand.
You can pre-check your fare:
http://www.taxi-calculator.com/index.php?tariff_id=178
MyTaxi is an app to call a licensed taxi, which has to charge the official fare.
Uber is restricted to limousine services, as a private driver is not allowed to carry passengers, and a licensed taxi driver would loose his license.
The only downside I have noticed during the last years is the growing number of foreign drivers having insufficient knowledge of German language and the streets in Vienna. The latter is compensated by navigation systems, because to pass the exam for a taxi driver's license you must know about 2000+ streets (out of 6800+).
Should you have any reason for a complaint, just put down the license plate number and report the incident to the Viennese Taxi Guild ("Wiener Taxi-Innung").