In my opinion, 'Pride and Prejudice' is one of the best. It has a great story with Elizabeth and Darcy's relationship development. The characters are so vivid. As for the worst, that's a tough call as all her works have value, but some might find 'Northanger Abbey' less engaging as it has a different tone compared to her other novels.
The best Jane Austen novel has to be 'Emma'. The character of Emma is so complex and interesting. She is headstrong and yet endearing. When it comes to the least favorite, it could be argued that 'Persuasion' might be considered by some. It has a more subdued and melancholic tone compared to her other works. But that doesn't mean it's not good. It's just that it might not have the same level of immediate charm as some of her others. But upon closer reading, one can find the beauty in its story of second chances and lost love.