Fruit is generally uncountable, but when we talk about types of fruit it becomes countable. So, the second is correct.

Hi, S.P! The correct answer is the second sentence: "My favorite fruits are bananas and oranges." Although "fruit" itself is uncountable, TYPES of fruit are, and in this case (as with many other items as well), English can shorten "types of fruit" to simply "fruits." Thus, while we're saying "my favorite fruits," we really mean "my favorite types of fruit." I hope this helps answer your question. Please let me know if it doesn't.