which year 3 series gives the best bang for buck and maitenance cost?

i was looking at an x3 but saw the reviews were not the greatest and even jeremy clarkson pretty much said it was not a good car...been thinking of a 3 series because they have been around for many years, which model 3 series gives the best bang for buck and maintenance cost and reliability? i know the new ones are super expensive to maintain (have to get new batteries registered at dealer or they explode...)

which year 3 series gives the best bang for buck and maitenance cost?