I cant comment on the individual schools and colleges you've chosen, but in my experience (I also had to choose between sixth form and college to study a levels) these are the differences:
(Note: I ended up choosing a college sixth form, so bear in mind I'll be biased towards that)
- School sixth forms are a lot like, well, school. As you're only taking so many a levels, you only have so many classes per day. Like you might have History at 9am, Psychology at 10am and Geography at 1pm. However, at school you have to come in for the full day. So if your last class ends at 2pm, and your school normally closes at 3.30pm, you have to stay until 3.30. One school sixth form I know let's students leave after their last class IF they are volunteering that same day. Otherwise, they can't leave until 3.30. College, however, treats you more like an adult. If your first class doesn't start until 10am, you don't come in until 10am. If your last class ends at 2pm, you can leave at 2pm. You get more flexibility with your time. Ask the schools what their policy is on when you arrive or leave, however, as they may let you leave after your final class. Like I said, everywhere has different policy.
- It's different protocol for different schools and colleges. The school sixth form I considered you had to wear smart work clothing, but the college I chose we could wear whatever we wanted. One girl literally came in onesies. A different one every day. However, some schools do allow you to wear what you want and some colleges insist you wear smart clothing. So, again, ask what the uniform policy is.
- Like uni, at college you call your teachers by their first names. At school sixth forms, you tend to still call them Mr or Mrs.
I can't think of many more examples. Because of exam boards, etc, classes and subjects are mostly the same. Another commenter on this thread said that college is a lot more like uni, and I'd agree with that. But I'd add that school sixth form is, school.
Personally, at 16, I enjoyed having the freedom to come and go as I wanted, wear what I wanted, and almost everyone had a part time job because we had the flexibility. We could work, e.g. Tuesday's at noon, because some people had no classes on a Tuesday. Whereas school sixth formers don't have that flexibility.
But it depends on the sort of person you are. If you want to do really well at your a levels, but you know you're not the type of person who puts in much individual work outside class, school would be better as being forced to stay for the whole day means you actually have to revise as there's not a lot else to do. I'm sure my grades would have been FAR better if I'd have stayed at a school sixth form to my college one, but I really enjoyed the freedom I gained with college.
Apologies for any grammar or word mistakes on this post. I'm typing on my iPad, and TSR likes to use autocorrect. I hope it all makes sense.