HANDS down, BMW’s most important model is the 3 Series with the least costly engine and a few expensive options thrown in. In the latest E90 guise that would be the 320i, the four-cylinder sedan that takes over from the hugely successful E46 318i. It’s been this way since the old E21 version released back in 1980. Twenty five years on, does the four-pot Three cut it in the fiercely competitive $50K-plus-prestige segment? (320i Executive sedan pictured)