Durham vs Edinburgh Vs York

Define "better" as in better unis and why do you think it is important to go to a "better" university?

If the answer is job prospects then that is the wrong reason. If you know that the teaching / support / extras / employability at one university is better than another then absolutely go for that.

For me, if I had my time again, I would definitely take a gap year and use that time to work a little and travel and most importantly discover a little bit about who I am, what I like and then I can use that information to take my next step. I can't help but feel too many people do what I did and jump onto the conveyor belt of life because that is what is expected despite it bringing little personal reward or satisfaction.

Good luck!

More just curious for opinions and reasons as im very stuck atm :/

CS or CS And Maths for all, curious on which to firm not scottish,and AAB-ABB offer grades, or gap year for better unis. Opinons?

Edinburgh is by far the best of those 3 for Mathematics. It's 33rd in the world for it on QS Rankings. Next best is Durham (201-250), then York (251-300).
For Computer Science, Edinburgh is 20th, York is 198th, and Durham is 301-350. I can't work out why Durham is ranking higher than Edinburgh and York for this on www.thecompleteuniversityguide.co.uk. In the case of Edinburgh, it appears to be purely because of student satisfaction, perhaps aided by the fact Durham got a new building recently. Durham have not historically been great for Computer Science. And York, for whom I hold no general candle as I was there when it was incredibly tired looking in the late 1990s, seem to be below Durham on CUG largely because of student satisfaction and entry standards. Computer Science is a subject for which York seem to be genuinely good - they got a nice building at a time when most other departments were making do with 1960s CLASP (and it appears that they've since moved to a newer building on the newer, adjoining, campus).
This is a clear win for Edinburgh.
Which universities do you regard as notably better than Edinburgh for these subjects?

I have since firmed Edinburgh due to reaching most of the conclusions previously mentioned and my own research, in regards to better its mainly down to Oxbridge and Imperial, and im 90% sure my guilt comes from never applying as I severely regret not having the opportunity to at least try, especially as I perform well on the MAT for the one or two times ive attempted it, at the moment the focus is kind of just on the A level grades and making an informed decsion on results day

Between the three, hand on heart, I would go for Edinburgh. I'm not a Scottish student and I have absolutely no bias towards it. All three are great places to study CS but in my opinion, I reckon Edinburgh should come top of your list of three, Durham second and York last.
Now with a gap year, where would you be looking to apply for "better" unis? I'm guessing you're looking at the likes of Imperial and Oxbridge, right?
For this to happen, you need to achieve 2 A*s A as a minimum to be in with a decent chance of getting in (minimum entry to Cambridge but I think Oxford is 1 less A star). So focus on your A levels! You should decide on firm and insurance based on your personal preferences. Rankings will say some things about each of the universities but at the end of the day, it's what you feel about the place.
Now, I got into Imperial this year to study Computer Science (Cambridge rejection). The admissions process at both is SUPER competitive with Imperial being more competitive between the two (1 in 17 vs 1 in 13 at Cambridge. Oxford has similar numbers to Imperial but the department is way smaller because it's sort of split between the joint honours courses with Philosophy and Maths so a massive department isn't really needed). Cambridge and Imperial now both require the TMUA for 2025 entry so if you plan on applying to both, you NEED to smash that admissions test.
Also, if you plan to take a gap year, you need to show them that you haven't just fallen off and have put your gap year to good use.
I would advise against a gap year (after briefly considering it myself) because I'm sure you would still be as happy at Edinburgh, Durham, York and the other places you applied to and you not only risk losing out on these offers but also, you might not get into these competitive courses at the likes of Oxbridge, Imperial, UCL, KCL etc. However, if you think that you can prove that the gap year was for improvement purposes, you should be OK. Also, if you do get an offer from Cambridge, they make you sit the STEP to check that your Maths hasn't fallen off.
I loved the facility at Durham and it was a nice and quiet town but there isn't really that much to do. I mean, on the Open Day, you don't get that vibe because of the crowds of people but I went to Durham in Year 11 just before exams to visit some family friends and the town centre was really quiet but it was a nice atmosphere.
I haven't seen York Uni but it ranks a decent bit lower than the other two for CS so may be worth considering.
Edinburgh in my opinion has everything - city vibe, quiet vibes, green spaces, architecture and many other things.