I would say that you should think about practicalities.
Does your child want to live in all three years? Do they want the option of doing at least some self-catering? Look at accommodation options for 2nd and 3rd years which will be different for all colleges and at the facilities provided within the college if they are likely to want to make their own lunches etc.
Are they likely to qualify for any extra help (eg some colleges do discounted termly meal passes for those with a household income below a certain threshold or offer travel grants etc)?
Would your child like to be right in the centre of town or OK with being a bit further out?
Has your child got a specific reason for applying to a particular college (eg mine got awards in a competition related to her degree choice run by the one she picked)?
Having said all that, maybe just go and wander around and look at some of the colleges and see if there is one that especially appeals for any reason. They have different architecture and a different feel from one another.
Plus, in fact, there isn't any guarantee of ending up at whichever college you pick since you might be reallocated, and it is perfectly OK to put in an open application if you have no particular feelings in any one direction.
My brother did Maths at Merton in Oxford and picked it mainly for this so absolutely not a rigorous evaluation of all the pros and cons: https://www.thatoxfordgirl.com/post/merton-s-annual-time-ceremony-a-very-oxford-tradition
Best of luck to all with interviews!