While I don't particularly feel good about the business model and lack of employee rights etc, one thing I prefer Uber for over Black Cabs is the pollution.

Many Ubers are Toyota Purises. Black cabs have 2.7L Diesel engines which contribute to London's terrible air quality.

Especially as I often see black cabs without passengers driving around - not sure if the're looking for rides or not, but there is no reason for an Uber driver do be doing the same - I see them waiting with the engine off.