Both have their advantages and disadvantages. I lived in a host family for four years when I was studying, but I was lucky to meet a good home, so I didn't change it for four years. Some of my classmates also met a family with bad personality or a lifestyle that is incompatible with you, and finally had to change their homes. This is the disadvantage of living in a host family. After all, being in someone else's home, there must be a lot of inconvenience in life, and there will be a distinction between subject and object, unless it hits it off with home, but it is unlikely to go for a short time during the summer vacation.

Of course, living in a host family has many advantages. You can observe the daily life of the British people at close range. Seriously, if you don't live in a host family, you can't live in a house like theirs all your life, which is quite interesting. That will be of great help to your oral English. If you live in school, you should live with the students from China who go with you, so you won't have a chance to practice your spoken English.

I have never lived in a dormitory, so I can't give you much advice. In fact, living in a dormitory doesn't mean you have much private space. Except that most university dormitories are single rooms, high schools should all be shared.

In fact, I still suggest that you live in a host family. After all, it won't take long to study abroad, even if you can't get used to your home completely, it doesn't matter much, but you still get the benefit, which is a time you may never have a chance to experience again in your life.