For anyone reading this, I would pick Aberystwyth for the place. Aberystwyth is a nice town, homely feel and the Victorian architecture is lovely, and the seaside area is very nice, in the warmer months paddle-boarding and canoeing and swimming is very popular, and popular student culture is bonfire nights on the pebbled beach socializing and playing frizbee and having a barbecue etc. Also the surrounding area is amazing for nature lovers. There is a small hill in Aberystwyth itself called Pen Dinas hill which is a nice casual stroll. It is within walking distance of the university accommodation, as is the whole town, which is very nice. Cardiff is very overrated - average city at best and is very depressing of a city. Also there is a sense of campus in Aberystwyth and the campus is very pleasant and very green, whereas Cardiff has a city spread out campus with no greenery. In terms of which university is best, that depends on each subject. I know journalism in Cardiff is meant to be amazing - 2nd in the UK as of 2022 I believe. But for Politics for example, Aberystwyth is much better and is renowned for being very high quality. Generally Aberystwyth ranks higher than Cardiff in university tables.
Cardiff has a slightly livelier night scene, though Aberystwyth is a good vibe at night as the nightlife is packed into a confined area whereas in Cardiff the pubs and clubs are very spread out so it lacks the atmosphere Aberystwyth has.