I have flow Sabena Airbus and Boeings many times. The airplanes are clean and well maintained. Not first class, but OK.
Although the Airbus is a much newer aircraft, personally I prefer the Boeing. The Airbus LOOKS more spacious inside, but once you take your seat, the actual space YOU have is about the same. The Airbus seats are more flimsy and I have found them broken or misadjusted more frequently than the old Boeing seats.
The Boeing is more noisy in the back of the cabin, but in the front and over wings the noise level is similar.
Also, when taking off or landing, specially if the runway is less than ideally flat, the Airbus shakes and rattles a lot, while the Boeing is rock solid. Similar to driving a Renault or Citroen vs. a Chevrolet Suburban on a rough road. Both airplanes are good, but the American engineering has a more solid feeling.
Finally, for such a short fly I would not bother to pay extra for a C-class. You are going to be in the air only for half an hour or so.