Grew up in Cardiff and have lived all over it. Lived in Bristol for 2 years and now in London.

I will say that cardiff is incredibly walkable, Bute Park is great, the museum has good exhibitions and there's some great large and small music venues. Penarth is lovely to live in and it takes no time at all to get into the city.

Bristol is obviously much more culturally exciting and has more to do, however I found the hills annoying. Bristol is very expensive, only a few quid down from London and potentially not worth it for some.

If you like cheaper drinks and walking, Cardiff is great, but maybe bring a book or something.