Far better the E220 CDI. I was driven into London in one last Tuesday that had done 75k miles in 2 years and still ran perfectly, giving 55mpg on the motorway. The 2.1 Mercedes diesel is more reliable than BMW's N47, though you probably won't have any trouble over its first 2 years. Both these cars will soon be replaced by new models, which is the reason for the favourable deals that are based on purchase discounts of as much as £10k.