I have driven BMW 5 series in USA and Mercedes C series in INDIA. If you ask me about the interior then surely Mercedes is the winner. Seating in BMW 5 at first time surprisingly it wont feel a luxury car at the back with its plastic and leather finish, only front seat can give you a better feel.
While comparing Merc's C series with BMW 5's interior, first one is much better with leather fabric stitch, plastic finish . Ride quality can't really compare coz , one was driven on USA road and the other was in INDIA. But I think Mercedes engine is little quicker.
I heard from the BMW owner in USA that suspension and maneuvering BMW is much better than Mercedes.
Looking or comparing exterior Merc's & BMW both are really superb. But I had 10% more deviation on Merc's
No Idea on Audi. But I don't think A4 is VFM
at that segment level.