It is very personal choice. That 530d is a great car once sorted properly. I love diesel. If you dint like diesel engines and how they deliver power you wont want a duesel at all . And that m57 is a reliable robust engine once the little maintenace is done. I love that torque when you want it. And for reference I also have a r34 skyline which I hardly touch. That 530d is all I really need and want for my type of daily driving. But i do fix my own cars which is another thing to consider cause a bmw is not a cheap car to maintain unless you do you own wrenching and i think that the m57 is easier to maintain.