The accommodations provided by Cardiff University are your bog standard uni halls. Shared bathrooms are not always ideal, but cleaners come in at least once a week and give everything a good scrub. Some of the buildings are a bit outdated and in need of some repairs, but the same is true of most university accommodations. Although I have heard that Talybont South has a pretty bad damp problem (I've never been there myself).
As for social life, each hall has its own reputation but on the whole everyone is friendly and gets along. There will be noise, sometimes at odd hours of the night on weekdays, but this is part of student life and security will usually shut down any parties that get too rowdy. I was in University Halls for my first year and despite the distance from the main uni buildings (1.5 miles) I had a good time. Uni Halls is one of the biggest halls of residence so you will get used to doors banging and people chatting at all times day or night. There is a free bus service run by the uni from the halls to Heath and Cathays campuses, but this only runs hourly and can get quite packed.
I've heard from people at Aberconway and Colum Halls that these two can get noisy due to being on a main road used by students, but again that's something you'll have to deal with wherever you end up. Gordon Hall is one of the smaller residences and is part-catered, and is on a quiet street but has a pretty good social scene. The Taly residences all have reputations for being party halls, but to be honest every hall at the uni has at least one party going on at some time.
No matter where you end up living and whether you get on with your flatmates or not really doesn't matter. You don't have to live with the same people next year and you don't have to be best friends with everyone you meet. Living in student halls is an amazing experience and makes adjusting to uni life that little bit easier. Just try and be considerate of other students, but most of all enjoy your time here at Cardiff Uni!