It seems unlikely it'll ever challenge the various versions of the 737 in raw numbers(*) but it has long ago passed the DC-9/MD-80 and 727 and is comfortably the second best-selling jet ever. Not bad for their first attempt at doing a narrowbody!
(*) But it's MUCH better looking than the 737!
(*) And I'd MUCH rather fly on an A320 that a 737!!
But hats off to both Boeing and Airbus. No-one can argue with the success of either the 737 or the A320!