I think at college you get a greater freedom and often range of subject choices - they can be aimed more at less academic qualifications. There's often no uniform or lower school kids. Personally however, I am sticking with my school sixth form as I love the school, all my friends go there, they offer the choices I want, I already know the teachers and I'll have a greater chance of positions of responsibility eg prefect. Some of my friends however want to take more b-techy type courses, hate the "claustrophobia" of school, think having to wear uniform sucks, want a fresh start/meet new people etc.
I hate the opinion that some people say Sixth Form College is for less academic people. Sixth form colleges still offer a levels as the majority choice. Sixth form college is NOT like a vocational college. At the end of the day, the majority of students will be taking A levels and aspiring to university. So I don't think people can state that Sixth Forms in schools are more highly respected, because in some instances the Sixth Form College achieves higher results than the school Sixth Form.
I didn't have a choice as my high school didn't have a sixth form. I'm quite happy at the sixth form college - it's nice to have new surroundings and teachers. The majority of the people here with me are doing A Levels or BTECs. The more vocational courses are run by a seperate college where I live... which means the majority of people at the college don't disrupt lessons like they did at high school.
Plus I no longer have to wear one of those stupid blazers whatever the weather. My jeans have never been so loved.