These can be difficult and confusing times, with everyone putting together well justified cases for their particular suggestion, the problem is, they are all different. There is no right or wrong answer, but the eventual choice has to come from your son's heart.
Some people prefer to maintain the academic momentum. Starting a job (or having a gap year) will break this momentum. The prospect of going back to studying after beginning work could be difficult for some, especially if money is an issue and they become used to a regular wage.
Alternatively, if your son has become totally jaded with studying, a gap experience or starting a job could reinvigorate his desire for learning. This is especially true if he ends up doing repetative or menial work !!
I opted for a compromise when I finished my A Levels. I found a Company who were offering to sponsor me on a 1:3:1 sandwich course in Aero Engineering. That meant that I started work on a decent salary after A levels for one year, got supported by them for the three years I was at Uni (which also included eight weeks worth of fully paid work in the summer) and had a further year of focussed work training after that. The regular college sessions in the first year of work ensured that the academic momentum was not lost.
Do I wish I had taken a gap year... sometimes, but I needed the money, so it was the right choice for me then. I've now seen most of the places I wanted to see back then, but probably with more luxary now.
Like I said before, there are no right or wrong answers, and I've probably just confused you and him even more. The only answer can come from your son when he has imagined himself in all three scenarios and decided which one seems to fit best now.
PS I'd be interested to know which route he eventually decides to take !!