former pedestrian, biker and taxi client here :)

"OK" are the biggest taxi company and because of that their quality varies
years ago, they were the best choice, they had the best cars and polite drivers
now .. it depends on which driver you stumble upon

I used to use them a lot,
but
actually
my taxi company of choice is Yes&amp;Yellow: they usually are politier (I know ... I just love making new words from errors ), were the first ones with GPSs in all cars, have smart messaging system ( no need to listen to noisy radio chats) etc

I am not sure about their english though ..

Yes &amp; Yellow phone: 02 / 91119