I live in Cardiff, and the city is lovely. It's large, but easy to get around. There's loads of places to visit - Cardiff Castle, Penarth Pier, Cardiff Bay, etc. The city really welcoming towards students too, as accommodation is cheap, there are loads of social events within the university and everyone who goes there seems to have a great time. The university campus is beautiful and it's about a 5-10 minutes walk from town. The medicine course is CBL, you get a mix of lectures, small group learning, patient contact, etc. You get placements around Wales so you can experience both city hospitals and rural hospitals.
The course at Birmingham looks good, it's mainly lecture based. The university campus is great as the medical school is close by, but the city centre is about a 30 minute bus journey away :/ The city is great as well, second largest city in the UK, loads of places to visit.
I've never been to the Barts campus but I've been to Queen Mary, and the atmosphere seemed really depressing, there was a cemetery on campus, and the campus was situated above the underground so you could hear and feel vibrations of the trains. Didn't really appeal to me :/