hey... no matter what car you buy from the BMW Stable, you are getting a Ultimate Driving Machine !!
all models have a thing in common - power and handling, even with a e9 or a e90, it drives like a dream, so think what you like, follow your dream and likes of which model suits your budget & daily needs then buy it !!
To me, if you are entering the bmw marquee for the first time, buy a used model, dun care which type, get a good one - and move from there !!