Which oil do I use in my A3 TDI (not PD and not AVS)?

I use Mobil 1 Turbo diesel in mine at the moment but i am considering using millers due to the cost of mobil 1 and that i will have to buy two next service. mobil comes in 4 litre wheras millers comes in 5 litres
 
I had thought about Castrol Magnatex GTD - any thoughts on this?
 
A decent 5w-40, carrying the code VW 505.00

Cheers
Simon