What is season 3, 4, 5, 6, 7 of Gilmore Girls Generally about?

Please be specific. My sister loves this show so im getting it for her for chrsitmas. i know she has watched some of the seasons but im not sure which one. i want to get the season that is the best one and one she hasent already seeen. Also please tell me what season is your Favorite. Please and thank you. Merry Christmas, Happy Holidays!!!!!!!!!!!!