Hey. I've highlighted some key points in your post.
you've hopefully made up your mind now where you want to go, but i'd advise you to go to the better sixth form college. i made the mistake of going to my schools sixth form (one of the best in my area) and now nearly half a year in i've applied to go to another college which has better overall facilities and hopefully enrichment.
Draw up a list of pros and cons of each college. Yes there is the transport issue, but are you able to apply for a travel bursary at all? anyone you could share a lift with? carshare? on travelling distance you may have to take revision material such as flashcards which you can revise with on the journey so that time isn't wasted.
Enrichment and facilities i would say are
important in some respect. See what each college has to offer. School sixth forms will normally be attached onto or inside the school, so you may still have to be with the younger kids, but you would be on the same level as teachers as respect goes... If there is little enrichment your schools 6th form offers you could find it only offers volunteering in lessons in main school and helping out in lessons. which is okay if you want, but see what clubs and activities both have to offer. Also see how big each college is compared with each other. If there is a tiny library for sixth formers who are revising for exams which is shared with a bunch of kids spending their lunch break, it is going to be packed of 6th formers in a noisy cramped environment. choose wisely.
Next, listen:
you will make new friends at where ever you will go. at the sixth form college people hopefully will come from a mix of schools from around the area. If you haven't been to an open day/evening
go to one. talk to current students in years 12-13. from them you can hear their accounts of the sixth form. You will find peoples friendship groups will change as you go through the 1st year of 6th form. It might be quite clicky at a sixth form where people have known each other since year 7, coming up the school together. so if your friends are moving on and you don't have a wide friendship circle you may find it harder to make friends, but there will be other new people at your sixth form as well.
finally, another point which you may not have considered, is what other subjects do the colleges offer? and are the grade requirements high for other subjects? if medicine doesn't work out for you is there a plan b? you need to do well in most of the academic subjects like geography, history, and english to do essay subjects at a level, otherwise you may only be left with softer subjects as essay subjects may be difficult. this depends of course.
some sixth forms are stricter and others, and oh then theres the dress code as well. some may be stricter than others.