I would recommend deciding whether you'd prefer self catered or catered to begin with. Then pick a couple you really like the sound of and visit those but then also visit one of the least popular ones that you think would still be ok (you can google some stats or just look on threads for how distressed people seem when they get their allocation). Because of the way they allocate if you put all the popular colleges at the top and your name doesn't come up near the top of the random selection you run the risk of not getting anywhere near what you'd want(could end up not getting your catering preference)...hence the unluckiest ending up at their 15th preference but plenty seem horrified by their 8th choice. If you can consider something not so popular that you'd still be ok with and put it say 3rd on your list they will hopefully still have places at your 'backup" if you aren't lucky enough with your 2 favourites rather than risk missing out on your catering preference(or whatever is most important to you) altogether. So...consider which you feel is the best of the least popular to you and visit that as well as a couple you love the sound of. Of course if you like all the least popular ones then you should be fine 🤣
My son wanted catered, we visited Johns, Chads, Marys Trevs & Aidans(open day & offer holder day). His preferences went Johns(desperately wanted), Chads(liked the look of and fancied the Bailey), Aidans (thought it was ok and liked its location/views & facilities so though it would be ok despite not being Bailey & gowned) He got Aidans so although gutted not to be Bailey he was very pleased he didn't end up self catered. He has actually loved it way more than he thought...and that is a pretty common thing, once they get there the overwhelming majority seem to love their College and can't imagine themselves elsewhere after a couple of weeks.
Hope that makes sense - good luck 🍀