Okay I just read some of their recent articles on the subject. They are completely full of shit. Why? Because they use two criteria and two criteria only. One of them is the price for a single ticket. That doesn't tell you how good the public transit system is, it tells you how expensive it is. Regular users of public transit don't use those tickets anyway, so this criterion is moot.
The other criterion is departures within the municipal limit per number of inhabitants. This isn't just stupid, it's pants-on-head retarded. By this criterion, you can just put down a dozen bus stops within disances of a few meters, put up no timetables or shelters and have a few buses run through once a minute with nobody using them and rate A+ on their chart.
They wank over Dresden's tram system being amazing, yet the average speed is 20.2 km/h, slower than the slowest line in Cologne (22.4km/h) and almost as bad as the slowest line of Hannover (19km/h). Both Cologne's and Hannover's Stadtbahn systems have lines with 30 to 35 km/h average speed. They rank worse because they have more centralized systems where multiple lines are bunched in a single tunnel, larger vehicles with more capacity and S-Bahn systems covering lots of the city and connecting to the surrounding urban area.
Their results are stupid. They rank Osnabrück, Wiesbaden and motherfucking MÜNSTER higher than Bielefeld or Hannover. I recommend the authors travel to those cities and see what it's like to get around a city of more than 300 000 people with nothing but BUSES themselves.