What city do you feel you would most enjoy living in for 3+ years? Choose that one. I work in a sector involving engineering, science and policy.. Speaking as somebody who regularly recruits and interviews for my employer, we look at the grade you got and not where you got it from generally, as well as how you do in your interviews.
Generally, in most industries/sectors, we have more importance on you having a STEM degree with a decent grade than the in establishment issuing it. Both are excellent universities.
We've hired people with good degrees from Swansea, Wrexham and other places and rejected people from Cambridge, Loughborough and Oxford int he past because the former impressed in interview and assessment and the latter didn't impress as much.
3+ years is a long time to spend in a city and it's important to choose somewhere you can both afford to live and enjoy living.