When i think of quality i think more of reliability in machanics rather than chasis. So there is rattles which has to do with insulation, this is difference than say the screws are loose or poorly assembled parts.
When i was test driving the cars before i bought the lexus, my criteria was that the car must be strong, has all the features i wanted, looks and feel good to drive and most importantly mechanically reliable. My previous car was the 5th gen Honda Prelude and although this car was perfect in the engine department, it had bad gearbox and what they called it shock knocks (from inadequate rubber insulation of the shocks). I have managed to solve the shock issues but the gearbox was what really made we want to sell the car. I could live with the knocks but could not live with the grinding of the automatic gearbox.
I made a choice not to get the BMW for a few reasons, one of it being the lacking of power and the experiencing of gearbox issues (yes i've driving a few e90 3 series and their gearboxes were on the way out already). Be warned, BMW gearboxes are not all that reliable, and neither are they smooth.
Ultimately it would be your choice but if i were to get a BMW i would get a newish 325Ci (2004 up), the coupe just looks awesome.