There are good and bad in both sectors but imo, if you were to put the best state school beside the best Independent school, then the Indie would top the state school.
It HAS to fit your child though or it is a complete waste of money. Look at the child you have and really consider what they need to bring the best out of them.
Mine are completely different children,
DD, very quiet, but fiercely academic, driven and competitive, fits in with somewhat nerdy, geek,y independent friends with drive, her current private school (6th Form) has allowed her to excel, Prefect, Head of Debating, Subject ambassador etc. Her confidence has rocketed and the opportunities to excel where she is strong have been very good.
Her Prep school took her from a quiet, shy, child and gently but persistently helped her to come out of her shell, take part in discussions and school plays and give speeches to an audience. They found her intellect and developed it.
Particularly important as she has a chronic health condition and missed a lot of early school years. They were very accommodating of this.
But we looked very hard to find what would fit her, and have for years driven her 35 minutes each way to school and back daily.
DS, sociable chatty and a bit lazy academically but has lots of energy, his Prep offered lots of exposure to music of all kinds, he has been playing an unusual instrument for 10 years now and loves being part of an orchestra. He was taught every sport imaginable and decent academics. But was bullied eventually, so we removed him straight away, and he went to a tiny Prep with little facilities but really good academics, which prepared him for Senior school.
We decided on a family feel co-ed small Private school with solid academics but a very warm inclusive ethos and it has been great for him, rebuilt his confidence, and he has a great group of friends. He is now confident enough to look at a more academic 6th form nearby.
Each school has given them something important, and built their characters in a very positive way, we listened to their input and reacted accordingly, but always made the final decision. It gets easier as they get older and their personalities shine through.
I do not like the rather woke leanings of some state schools, and wanted both to have the aspiration and character that we believe in, luckily the schools have done this admirably.