Basic English Usage
Once again, pay close attention! This is subtle stuff, but you will read it in the writing of many people, so try to learn it little by little.
When comparing things in the form "A is * better X than B is" use the word a in front of the comparison:
Liu is a better student than Lee is.
Shanghai is a busier city than Suzhou is.
When comparing things in the form "between A and B, A is * more X" use the word the:
Between Liu and Lee, Liu is the better student.
Between Shanghai and Suzhou, Shanghai is the busier city.
When declaring something to be the best, use the word the:
Lee is the best athlete.
Suzhou is the best city for buying fine silk.
When declaring something to be the best using the form "of all the X, A is * best" use the word the:
Of all the gymnasts I have met, Lee is the funniest.
Of all the cities I have seen, Suzhou is the most beautiful.
Course: Basic English Usage