Hi and welcome.
I’ve also got an S60 2.4 D5 and I love it too.
Tyres are subjective, when you say “best” to me that means best value for my needs, my car is used mostly driving around my city, commuting to work, shopping trips, visiting friends, so I don’t need a premium tyre because my car isn’t driven to its limits. I have bought all makes of tyres over the years and to be honest I can’t tell much difference between premium and budgets, the last set of Michelins (energy saver) I had were poor in the wet, they would easily spin but they’re good point was long tyre life.
Currently have Westlake’s SV308 fitted on 225/45R17, good all round tyre, no complaints, I could afford to fit mid-range or premium tyres but from experience, I just personally don’t see any benefit in doing so, but like I said, tyres are subjective!
edit: forgot to add link.
http://www.tyre-shopper.co.uk/