Hi!
A lot of people find the choice between college and sixth form difficult, but really the only person who can decide is you - nobody can tell you what choice to make!
Personally, I was a little torn (I ultimately went to college as the courses were more fitting for me), but I know how you feel with the 'leaving friends' situation. I ended up with all of my friends going to sixth form, and although I don't think I've made any more friends on quite the same level as the ones I had in year 11, I get on well with a lot of the people in my classes, and I'm still in contact with my closest friends from school! I hated my school and a lot of the people in it, so I found it super refreshing to be around a whole bunch of new people. A lot of people I know in a similar position have ended up with new best friends and such!
The way in which a school or college is managed is a pretty big thing in making choices, honestly; especially if you're planning on university, your further education experiences (both work and academically) can make or break an application. It's worth looking into the work experience and extra-curricular activities etc offered by each before making your choice. Also, if you don't get along with your teachers, it'll make it really hard to get the feedback and support that you need at A Level.
This is already ridiculously long, but I appreciate that this sounds a lot like I'm leaning towards college, so: the journey is important! I don't know where in the UK you are or how long each bus journey would take, but how motivated will you be to get up super early for what could potentially only be a 2-3 hour day? Also consider the delays of late buses (which is pretty common where I live), and the expenses; bus tickets can cost a lot, and not all colleges offer bursary options etc.
I hope this helped at least a little. Good luck with whichever you choose!