The F30 is the first BMW I owned, so I cannot talk about the E90. However, I would have never bought a BMW if their new car were still the E90. I never liked it. Never liked the interior and was not too crazy about the exterior either. I was a Mercedes fan right until the F30 came out.
Maybe you guys know best when comparing the two, but for me, the best 3 series to buy is by far the F30. I love everything about it and this car brings a smile to my face every time I am driving it. Isn't this the most important feat of a car?
Yesterday I gave my car a wash, it was beautiful outside and in my lunch break I went to clean it. While I was removing every water drop still left on it, people stopped by to admire the car. I got a few compliments and even one driver with an E90 stopped to say "nice car buddy". Needless to say how proud I was...