I think ultimately the decision has to be up to you. Before I started 6th form, I was in a similar dilemma but think I did make the right choice in the end.
School A for me achieved the best or some of the best results for that type of school in the county, all my friends were there (and it'd taken a long time to make them), I was told they'd tailor my timetable for me etc. School B was an Evangelical Christian school (that was difficult because they forced everyone to go to chapel every day and were v homophobic openly etc but most schools aren't like that legally anyway), good results, some of the best in it's county (different counties) and offered a subject that school A didn't and it was a subject that was fairly light and one I really wanted to do - useful for my uni degree but not necessary.
I ended up choosing School B in the end although it was a difficult decision. I think the thing that really got me was that going to uni, my friends and I would have to move anyway. I made a few new friends, not as many as I could've but they're really close friends and am in contact with some of my old school friends too. I actually think I wouldn't have got as good results had I stayed in school A because I would have been too familiar (especially with friends - although all really high achievers, because we were so close, studying was difficult around them) whereas because school B was unfamiliar, I worked harder and they had smaller class sizes which definitely helped (though were stricter which was annoying but...).
The campus was definitely more beautiful which idk was an added factor but although I missed a few things about school A, school B was quieter, more focused and I grew so much more as a person in a new environment in a way that I definitely couldn't have in School A. I still achieved 3 A*s etc and got into the unis I wanted (one uni has an acceptance rate of 8%). I really did grow.
I think although of course results are important, results are only one aspect and often teaching is important, environment etc (for example one school I went to a few years ago, the results didn't look amazing but the teaching was some of the best I'd had - the results tables weren't as good just because it was a huge school with many more pupils so yes they got quite a few pupils brilliant results, it's impossible to get those results for everyone in such a big school with a range of capabilities) is too and although GCSEs results are often down to teaching, with A levels, you're expected to do a lot more independent work anyway although it helps if teaching is good.
As I said though, ultimately it is up to you and you have to go with what fits with you best. I personally decided that the positives of moving to school B outweighed the negatives and although the familiarity of school A was comforting and difficult to part with, I needed a change and grew a lot more in school B...