It's a tough decision, but ultimately you need to think about your future. Staying in school for Sixth Form might mean less independence than college, but there's time for that at uni (if you decide to go). If there's less pressure to revise etc. would that be a good thing for you/do you have enough self-motivation to achieve what you want?
Regarding teachers, the relationship between student-teachers changes so much in sixth form when they realise you share their love for the subject + smaller classes mean they know you better. If your school has a reputation for being academic, then that'll make uni applications etc. a lot easier, as A: they're experienced and B: the unis might recognise the school name and quality of students.
I don't think having to stay in school all day is a good enough reason to go somewhere else, and you say it would be a 'new start' there but if your friends (who sound toxic and not friends at all) are going there, it's not much of a fresh start.
Also, Open Evening is never a good representation of any college/school, they put their best feet forward and could be entirely false. I realise how biased this sounds, and it's up to you, but to me it sounds like school would be the better option.
Good luck!