Which orchestral instrument?

As another flautist I second this wholeheartedly!
I wish I'd chosen something else & steered my dd away from the flute for pretty much the reasons above.

I'm not convinced by the oboe/bassoon thing (maybe just because I don't love the sound!) - when I was at uni I played a stringed instrument in lots of groups. I wasn't the best, but I had the relevant standard and you always needed lots of my instrument so if you didn't get into one concert or ensemble another one would come along. But I remember meeting a bassoon player in the Gilbert and Sullivan society and she said that because you only normally needed ONE of them, it was pretty much impossible to get a spot and she'd had to join this (pretty low standard, to be fair) group just to get enough performance experience. I think she was actually studying Music too.

Actually though I think your DS should pick an instrument he likes the sound of; he's much more likely to carry on if he's motivated.

I've played violin, piano, clarinet, briefly flute. My brother played oboe and trumpet. I don't know what's most sought after. I'd choose something practical and enjoyable. Rather than worrying about competition, aim to be really good. Find out what he likes the sound of. Personally I dislike oboe, my brother didn't like flute.

I’d say brass, probably trumpet. My reasoning is the number of different opportunities to play. With the exception of string quartets, just about every type of music group has brass. There’s also a thriving brass band movement, so he’d never be short of groups to join and the social life that goes with it.

I'm not sure if this is an update of a book I once read, or a different one. But the one I read on this subject was really interesting.
https://www.amazon.co.uk/Right-Instrument-Your-Child-ebook/dp/B007RG9KB0/ref=sr_1_4?crid=3BLW54324X5QA&dib=eyJ2IjoiMSJ9.fRf3-N3HPY_gTzLZK0Y7ozQH9aeQXzmBt1wqw-i2tm_R9sVbjyAsKMccZ4f38u-E1bxL_ORkkv2NhdCSYukSdiKp8NBVOrYvy2CIZMN7X4UxMdB29I8zqdiLLlt1usHJEzf2NiwrbeV_tjVBIZaTrb8PofUtSuCBDqExpzacEVqpeJHXCPpfi9elyU79_Yx1n315psfB7dJwxLdkqRixZUsV16RsFD2itINx1fk2Hto.vCv7TEs0h1euwzfGCL4T7KofjpZuDLHcISqsjsATl_U&dib_tag=se&keywords=choose+your+instrument&qid=1719824787&s=books&sprefix=choose+your+instrument%2Cstripbooks%2C56&sr=1-4

Small and portable! Oboe, flute, too much competition on clarinet maybe? Nice thing about the flute is that in the early days when he's not very good it's still pretty inoffensive on the ear, whereas trumpet, violin etc, can take years for you not to want to throw yourself out the window during practice time!

Millions of second hand flutes on ebay too - I got my daughter a very good flute on Ebay for £150, but you can do even better. Pick an entry level one from a specialist instrument website, and then search for that model on Ebay and you'll clean up.

As a flautist, I'd say not the flute.I loved it as a young child (it's relatively easy, so you can feel you're improving fast) but now wish I'd chosen something else. My reasons:
1 (this probably stands for other non-string instruments too) I spend a lot of time sitting around in orchestra rehearsals counting bars rather than actually playing.
2 There are way too many of us, so no one is very grateful for our presence and conductors would really rather most of us weren't there.
3 It's not that adaptable - it just always sounds rather the same, compared to the different types of sound/music you can get out of strings, guitar, piano etc.

I'd always vote for piano and guitar as go-to instruments, but if you want an orchestral instrument rather than a band instrument, I'd go strings. Our orchestra (for crap players, not elite ones) always has a chronic shortage of violins and violas. They are playing pretty much constantly so they can't get bored, and they can play basic chords so it's not just one note all the time.

Was also going to suggest oboe. Sought after and not too heavy. (Also not as annoying)

There’s also fewer of the, needed and the standard and competition is higher after the early years.

French horn/ viola/ bassoon can be a way to go. Or percussion.

Try to find whether brass/ ww or strings appeal. Always need lots of strings.

Yes I had the same issue as a clarinet player, always had a spot in the school orchestra and wind band, but was third string for years as were so many players better than me!

From a purely practical point of view, something he can carry, so not a cello or double bass (even though he'd start on a smaller one I remember a scary moment when a friend was blown into the road as a tall teenager carrying her cello, it was like a sail in a sharp gust of wind!)

Instruments are expensive, do you have the opportunity to hire from school or county music service? My kids are adults now and we were able to hire to begin with, though I'm thinking school music service could well no longer exist due to cuts.

Is there the chance of him trying out strings, brass and woodwind, trial lesson or two, see what he likes the best?

Double reed instruments like the oboe are always more sought after in orchestras, and then when he's older could play basoon. There's much more competition for violin, flute and clarinet (I'm a flautist and you have to be really good to get a spot!).