This question, and its answer, are corroborated by Wikipedia – which describes the Boeing 737 as "the highest–selling commercial jetliner in history."
You might wonder, as I did, why the word "jet" is necessary (or "jetliner", rather than "airliner"). Surely the best–selling jet airliner is going to be the best–selling airliner of any kind? What with air travel being so common these days, and jets having been around now for more or less half of the time since the Wright Brothers were lads.
Then again, you could ask why the word "commercial" is neccessary. What other kind of airliner is there?
The answer is probably the military transport kind. And the fly in the ointment is probably the Douglas DC–3. This was designed as an airliner, but of just over 16,000 DC–3s that were built (between 1935 and 1952), only 607 were of the airliner variant; the rest were for military transport use.
You might still wonder why any distinction is necessary, given that I've just used the term "airliner variant" to describe the 607 DC–3s that were not built for military use. Well this is Wikipedia's term, and on this occasion I'm not going to argue. I might have misunderstood the whole issue – in which case, I do admit, I'm wasting both my time and yours!
Wikipedia has a list of most–produced aircraft, which is where most of my information comes from. The DC–3 is 17th on this list, and the 737 is 39th. I can see nothing higher than the 737 that might be described as an airliner, other than the DC–3.
Up to October 2018, only 10,314 737s had been made (compared to over 16,000 DC–3s). So the 737 is arguably not the best–selling airliner of all time; but it is surely the best–selling commercial airliner of all time, and it's also the best–selling jet airliner of all time.
The use of both of the words "commercial" and "jet" could possibly be described as overkill; either, it seems to me, would have been enough to separate the 737 from the DC–3. And I would suggest that "commercial" is the more significant distinction.
By now, you may be wondering what's top of the list – the most–produced aircraft of all time. So I'll tell you: it's the Cessna 172, which has been in continuous production since 1956. Up to June 2017, over 44,000 had been built (that's just over 700 a year).
Second is the Ilyushin Il–2, a ground–attack aircraft used by the Soviet Union during World War II – with over 36,000 built. Third is the Messerschmitt Bf 109, and fourth is the Piper PA–28 series. Cessnas occupy the fifth and sixth places, and Britain's most–produced aircraft is in seventh place: the Supermarine Spitfire/Seafire, with 22,685 built.
© Macclesfield Quiz League 2019