May I ask you what's your career goal and where you are from?
First thing is that you carefully read the entry requirements for the relevant courses, not all MSc Finance programmes may accept you with only having a minor in finance, and some only accept students with a first (for some countries it even matters at which university you have done your undergrad)
Then you can look at league tables, to get some indication, such as
http://www.thecompleteuniversityguide.co.uk/league-tables/rankings?s=Accounting+%26+Financehttp://www.theguardian.com/education/ng-interactive/2014/jun/03/university-guide-2015-league-table-for-accounting-and-financeMind these are not perfect either (and are more for when choosing your undergraduate degree, as most measures are based purely on measures from undergraduates), as you can see both vastly differ in their rankings.
Then, you can look at the staff in Finance in the respective universities, i.e. who would be teaching you.
You should also look at the course content, and compare those with each other, such as how much contact time, and what modules (believe it or not, but this too can vastly differ), and what facilities do they offer (not sure whether relevant for your intended career / programme but Cardiff got a nice trading room in which all postgrads can work in and do a separate course).
Tuition fees + living costs, how much can you afford? This again vastly differs. London being considerably more expensive.
You can also compare the cities with each other, i.e. do you want to live in bustling city like London or Birmingham, do you want peace and quiet? Do you want a campus university or a city university; or somewhere in between like Cardiff (got everything you want, is quite compact but doesn't all the excitements like those bigger cities)