Both excellent universities, congratulations on getting offers from both!
It so much depends on the individual and what they are hoping to get from the university experience. Assuming the course is similar at both, you will be considering reputation/league tables, and also extra-curricular opportunities.
Regarding the former, I agree that Exeter might be slightly higer placed, and therefore might look better on a future CV, but imo it appears to attract more students from the the South of UK. I don't know where you live, but where I am, it's sometimes called "Surrey-on-sea"! If your DS wants to meet students from a wider area, maybe Loughborough would be better as it's more UK central.
On the other hand, in terms of extra-curricular sports, Loughborough attracts very sporty students such that team participation might be limited. My DP's brother was a very good club/county rugby player, but was unable to make a team at Loughborough as there were so many very good players there. He ended up leaving after a year and restarting his degree somewhere else where he was able to fully participate in the rugby set.
If inclusive sporting participation and academic reputation is a priority for your son, maybe Exeter might be preferable, but if a more inclusive social experience is important, maybe go Loughborough.
I'm sure he'll be happy wherever he goes. Good luck!