Your selected universities have around 20,000 students each, except for Manchester which has almost 40,000; they will all have roughly the same mix of people and it would be impossible to find an institute of higher learning that does not contain extroverts, an anonymous poster on a student forum's anecdotal evidence should not influence your decision in the slightest. At the same time no-one is forcing you to spend time with people you don't like, establish a friendship group with like-minded people and avoid those who make you uneasy.