College help Watch
If really in doubt, you could look at which of those has been least competitive recently and go for that. Whilst that won't increase your chances of getting into Oxford, it might reduce your chances of being pooled to a college without, say, 24/7 library access.
I would focus on the following in addition to a 24/7 library:
Location (distance to your faculty)
Accommodation (for 3 years? prices? etc)
Kitchen if you want to cook yourself
If you're vegetarian also check which colleges have good veg food
How many tutors does the college have for your subject?
Is there a designated library for your subject?
Do you pay-as-you-go for hall or do you have to pre-pay? (whichever you prefer)
Personally having a bit of a similar dilemma to you. Will be applying this October to study law starting 2020 and cant fully decide between John's, Worcester and Brasenose. Leaning more towards Worcester atm.
I’m looking to study chemistry at oxford for 2020 entry and find myself struggling to pick a college. I know I can always do an open application however some of the colleges don’t have a 24/7 library and since I suffer with insomnia I feel like I’ll be doing a lot of late night studying. I’m currently looking at Exeter, Queens, St Anne’s and St Peters. I’ve visited them all and still can’t choose. Any help or advice would be appreciated.
2. Personally, I think one of the best parts of Oxford is living in the city centre, so that everything is a short walk away. Exeter keeps you onsite for first year, but I'm unsure about the remaining four. So check where you'll be living when off-site, and how far it is from your college's facilities and the city centre.
3. Try the college suggester: http://apply.oxfordsu.org/colleges/suggester/
4. Remember, though I think college choice is more important than the university says, they're all good and you'll end up somewhere you love.