Hi, I live in Adda at Ffiddoedd, but out of your list from there, I would recommend Llanddwyn, as the shop is in the same building on the bottom floor, the laundrette is right outside that building with both the security office and the halls/mail office is a one minute walk away from that building. In St Mary's there has been construction work going on there for a couple of months as it's still a new building, but I think it would be done by summer, I don't really know much about St Mary's, but it is a nice place, the people I know who live there haven't complained. It depends on what you are studying, as if it is in upper Bangor then you're going to have to go up another hill, so I would consider that.