I would not use either:
Tom is the most intelligent person in his family.
The USA is the best country.
Can I say "Tom is the most intelligent person in his family" or "The USA is the best country in the world"?
My cousin named Ann is the most beautiful girl among the female cousins I have. How about this? Is it incorrect?
Remember to look for repeated words in your sentences before posting them. Articles, prepositions, and auxiliary verbs may naturally occur several times in a sentence, but a repeated noun is often a sign that there's room for improvement. [I edited out a repetition of the word "sentence" while I was writing that.My cousin named Ann is the most beautiful girl among the female cousins I have.
My cousin named Ann is the most beautiful girl among the female cousins I have. How about this? Is it incorrect?
I should have called out girl and female, too. Synonyms may be a sign that a sentence can be shortened.Remember to look for repeated words in your sentences before posting them. Articles, prepositions, and auxiliary verbs may naturally occur several times in a sentence, but a repeated noun is often a sign that there's room for improvement. [I edited out a repetition of the word "sentence" while I was writing that.]