Hi OP, you have had some good advice on this thread but also some which is a little old fashioned.
I have worked in HE for 15 years, I’m not an academic or an admissions professional but I have some insight.
Ultimately, university league tables are created by organisations as a money-making endeavour. No one is doing it as an altruistic service to prospective students. Yes, having various different metrics in one place can help to assimilate the information, but if you put too much weight on something as artificial as a league table place or mission group you can go wrong.
Choosing a university is a very personal decision, specific to each individual based on their ambitions and interests. You are absolutely right to start with a subject-specific lens and work out from there.
Other approaches are practical: affordability, distance from home, housing/transport considerations etc. Also, wider lifestyle preferences: city or rural, coastal or inland, large uni or small?
Some people look at graduate outcomes - % in grad level jobs or salary levels. My view is that this is not entirely reliable. Universities with very middle class-heavy graduates will fare better overall. Universities serving a regional job market or the public sector will fare worse, but will still be great universities. Graduate outcomes are much more a product of our fucked up social mobility and economy as they are a measure of university quality (and the metrics are not amazing in any case).
The best way a student can guarantee great outcomes is to be born into a nice middle class family with good social and cultural capital. On top of that, students who really take advantage of everything a university has to offer will succeed. For example, my friend’s daughter has just started at Bristol. She has 8 hours of lectures/seminars a week, so she has plenty of time to get herself down to the careers service and find out all about the millions of employability / placements / internships/ extras that are available. Too many students wait until half way through third year when they are also juggling dissertations.
Finally, on the financial stability front, yes, it’s a worry. However, last week Jacqui Smith hinted that the government is minded to intervene to avoid a “disorderly exit”, so as long as you don’t pick the University of Del Boy Trotter you will probably be fine.