You make some very good points in your essay! I have just a few editing suggestions for you:
Big cities are where you can see many vehicles, many skyscrapers, and many people with a hurried pace of life.
Indeed, in a big city, people can have the best opportunities for work, as well as enjoying the best service and entertainment.
In a big city, people have the best chance to study and work.
There are many good universities to choose from in a big city.
Moreover, when you graduate, you also find it easier to find opportunities to get a good job with a good salary. That is quite difficult in small cities or countrysides, where there are not as many many big companies and groups. Hence, many graduate students choose big cities to live and work. In short, it is where you can take advantage of a city's benefits for yourself.
There are many rich people in cities, because they are a good place to invest money.
Lives in a big city can be quite luxurious and you do not have to be worried when you are sick or suffer a disease because you can find good doctors there, as long as you have a lot of money.
What's more, in a big city you can enjoy new entertainment such as new games or luxury games. - This is a little vague; what kinds of games? What do you mean by "luxury games"?
Many people can argue that living in a big city makes them tired with noise and dashing about.
However, when you get older, especially when you retire, the countryside is the best choice of places to live.
However, you have to try your best to overcome all difficulties such as hard competition in the workplace or a polluted environment. You should not complain when faced with the disadvantages of it. - Your conclusion is not the best place to introduce new ideas like competitive workplaces, pollution, or disadvantages. If you want to mention these things, talk about them in the body of the essay; otherwise, do not bring them in, for the first time, in the conclusion. Use the conclusion to summarize only what you have already said.
I hope this helps!