In my somewhat humble opinion, this is her best book. I first listened to this one on CD (Juliet Stevenson is the goddess of Austen narrators, if you get the book on tape or CD, find one of her versions). There is a part of sandington season 2 toward the end, where Anne Elliott, the protagonist, receives a love letter. It is not just a love letter, it is THE love letter. I pulled the car over, reversed the CD and listened again. So, I caused a seven-car pile-up, it was worth it. The 1995 movie with Amanda Root and Ciaran Hinds is excellent.
Sense and Sensibility - I think this is her darkest book, but you'll get a lot out of it. I see many parallels between this book and Becoming Jane. Elinor Dashwood is an exceptional heroine, her strength and resolve is inspiring. For a movie choice, I cast my ballot with Emma Thompson's version. She takes some liberties with the stories, but good ones. She edited parts out with utmost care and added a bit here and there to enhance the audience's understanding of this complex novel.
Mansfield Park - The heroine of this novel is the subject of much debate among Austen fans. Some find Fanny Price tepid and dull, but I believe that to be a low estimation of her worth. If you really give this an honest and thorough read, you'll find Fanny to be a wonderful character. True she isn't as flashy and fun as Elizabeth Bennett or Emma Woodhouse, but we can't all be lively and vivacious. This is a great book about morality and honor and discretion. I have no movie recommendations for this one. The 1999 version with Frances O'Connor was cast with some fine actors and the art direction and cinematography were first rate, but this heavily rewritten version is almost an insult to what Austen was trying to accomplish with her wonderful novel.