As someone living in Swansea, I would go for Swansea instead of Cardiff. The nightlife in Swansea is amazing and drinks are only £1 every Wednesday night in all the clubs. Wednesday night is student night so basically all the students go out mostly Wednesday night. The Swansea university is right next to the beach and only less than 10 mins drive to the city centre and buses run every 10 mins. The seaviews from Swansea univeersity are amazing. All the clubs in Swansea are in one street which is called Wind Street but in Cardiff all the clubs are scattered everywhere so on a night out in Cardiff u will have to walk 25 mins from one club to another which is not nice. Also there are lots of places u can visit near Swansea like the Gower, Mumbles, Tenby, Rhossili just mentioning a few. But obviously if u like shopping, Cardiff has got more shops than Swansea because obviously Cardiff is bigger than Swansea.