best oil?

More expensive doesn't always mean more better. Different diesel engines require Different properties in oil. Some may run best on a low SAPS, some mid and some high. What most people seem to completely dismiss when looking for oil is the HTHS rating (High Temperature High Shear). Low HTHS can provide better fuel economy, and higher HTHS can provide better protection for your engine, the tradeoff is the more you have of one, the less you have of the other.

I use an ACEA C3 oil in my mk4 Mondeo. Total ECS. even though ford recommend Acea A5 but Peugeot designed their engines and Peugeot recommend the ACEA C3 listed above. That's an isolated example and I don't recommend you do that.

I would ring a dealers or look in your service manual, its not wise to just go throwing any ACEA Cx oil into your engine, each diesel is different, and from what I gather each ACEA rating isn't compatible with the next i.e don't use ACEA C1 instead of ACEA C4.

Brand wise, I've commonly used Total oils and they've been my go to, but other oils can be just as good, used MPM, sold by top part before with no issues and have heard good things about other people that used it, I find castrol a bit too expensive for my liking but they're a well established company.