I reckon BP Ultimate diesel is the best, both for performance and for economy. Shell V Power diesel is excellent for the health of the fuel system, but in my experience it does not improve economy. You can get a variation of 5mpg between different diesel fuels. Diesel with inadequate lubricity can wreck the injection pump. Diesel with inadequate detergent can lead to blocked fuel systems and injectors. Be very careful when filling with Shell, BP and Total because their top petrol and diesel, and even Shell's standard Fuelsave are branded the same whether petrol, or diesel. Very easy to misfill with petrol.