Here in Australia BMW dearlerships used Mobil 1 up until the time BMW negotiated a global supply deal with Castrol. Now all BMW's oil is supplied by Castrol. While Castrol makes good oils I personally would be using Mobil 1. It didn't hurt a five series I had for the 12 years that I had it
. Owning a diesel I am feeding it a diet of a local company's oil (Penrite) which I am very happy with. However, I never ever let the oil be changed only at service intervals. The default setting is 15,000 kms between services and I think that's far too much, so mine gets changed every 7,500 kms. Any quality full synthetic oil that meets BMW spec will be fine.