There's a student room article somewhere on college pros and cons...
Anyway, my personal opinion:
Trinity Hall: Apparently has good accommodation + very good value, nice central location but hidden just behind Caius so gets less tourists
Sidney Sussex: I almost decided to apply here, it is a very nice college. Good central location, nice accommodation (with mini fridges in your room...), pretty old architecture, just opposite Sainsburys
St Johns: Massive college, good range of accommodation/ prices, great for extracurriculars/ socials, good academic reputation, sometimes has a reputation for being 'posh' and has some weird traditions like locking students in for formal dinners...
Magdalene: Don't know much, it seems fairly small and is just outside the centre of town, right next to the river. Probably not too far away to walk to lectures while still being convenient to get to the boathouse...
Emmanuel: Another college I considered applying to, it has a reputation for being very friendly (although tbh all colleges are), pretty good accommodation, good academic reputation, ducks...
Downing: Personally I really didn't like Downing when I visited, mainly I think because it seems a little strict and military-like from the outside (all 'don't walk on the grass' and very square buildings/ courts), it is very centrally located, apparently has good accommodation, I personally just didn't like the atmosphere...
Corpus: Very small college, pretty centrally located, very pretty but a bit cramped (courts are very small due to small plot of land I guess...), nice library
Churchill: in my opinion very ugly from the outside (although I few people love the architecture... probably a love/ hate kind of thing), the rooms are generally very spacious and well furnished with big windows and good value, the food is pretty good, pretty big grounds for sports, I think it has an observatory either within the grounds or right next door, good for extracurriculars, bit far out of town if you don't like cycling uphill, lots of science-y students since in it's constitution 70% of students must be studying STEM subjects.