Having been to both school and sixth form i can help i suppose.
Sixth form is very strict, many make you wear a uniform or suit, and they constantly nag you about homeowkr. You get free lessons but thats about the only freedom other than being allowed to go out for lunch. You may also get a common room but theyre not amazing in most schools... just a place top spend your free lessons doing your homework.
College,m however, is much more independant and usually better equipped for sixth form needs... e.g. more computers, better facilities, more freedom (can go home when you like) and they dont nag. However, the onus is on you to do your work and turn up etc because they dont care if you fail, unlike a sixth form which will be upset for you if you fail because it relflects badly on the school. Colleges dont appear to be quite so picky.
And to the poster above, teachers are usually there to help ALL the time at college because they dont have to teach the lower school, so they have more time for you... IF you want to learn that is.