Answer:
Polish - most Polish immigrated during the early twentieth century.
The majority of them settled in the Mid-western United States, especially in and around Chicago. T
The biggest challenge that they faced was due to their religion: the vast majority of them were catholics living in a Protestant-dominated country. Some of them were Jews as well, and had exactly the same problem.
Irish - Irish immigration reached its peak from 1851 to 1860, with almost a million arrivals, an impressive number for a small island. The majority of them emigrated due to the extreme poverty and famine that struck Ireland at the time.
The Irish settled mainly in the urban areas of the Northeast, particularly in Boston, New York City, and Philadelphia.
As catholics, they faced the same challenge as the Polish. They were also subjected to denigrating stereotypes, probably having to do with the extreme poverty in which most of them arrived.
Chinese - Chinese immigration had an early peak in the late nineteenth century, after which it was forbidden by the Chinese Immigration Act of 1923. After this act was overruled, they began to emigrate in important numbers in the latter half of the twentieth century.
The have mostly settled in the West Coast, particularly in San Francisco, but other major urban areas like New York City and Chicago have also received an important amount of Chinese immigration.
Because the Chinese culture is very different from mainstream American culture, they have often faced harsh discrimination, and the Chinese Immigration Act is a proof to this.