edinburgh is a really good uni, on majority of the league tables UCL is only a few spots above edinburgh. if international rankings are something you care about, UCL is internationally more recognised than edinburgh, but international rankings aren't extremely important
it depends on if UCL will give you significantly better job prospects, and if your degree would be worth a lot more if it's from UCL compared to edi?
it can be very subject-specific
if i were in your shoes i would go for edi, i do generally just prefer it as a city, but for me at least uni being free is something that would be very important to me, but it is completely up to you.
have you looked into the course syllabus for both unis and if u prefer one? also take into account the cost of living in the two cities, london will be more expensive by edinburgh, but i'm not sure how expensive edi actually is so not sure how different it will be
just some things you could possibly look into if you want to make a more informed decision