Official Maltese taxis are white (usually Mercedes, with a taxi sign on top; www.maltataxi.net). To combat regular complaints of overcharging, taxi drivers must by law use the meter to determine the fare (except from the airport and sea port, where there are set fares). At the time of writing, Uber was not available in Malta, but a local company eCABS offers a similar app-based service.
Details of the fixed fares from the airport are available at the taxi desk in the arrivals hall, where you can pay in advance and hand a ticket to the driver. These were the fares at the time of research:
There are taxi ranks at City Gate and outside the Grand Master's Palace in Valletta, and at bus stations and major hotels in the main tourist resorts. Within Valletta, Smart Cabs provides an electric-powered taxi service for a flat fare of €5/8 for three people inside/outside the city walls.
As an alternative to the official Maltese white taxis, unsigned black taxis are owned by private companies and usually offer cheaper set fares (similar to the UK's minicabs). To order a taxi, it's best to ask your hotel reception for the name and number of their preferred service. There are several 24-hour companies.
Wembley's Reliable 24-hour radio taxi service offering both cars and minivans. Prices are often slightly less than other companies.