@cariadlet
Well Lydia Bennett has a personality which Kitty, arguably Jane and lots of 19th century women in novels don't. And her personality is better than Mary's. Plus 15 year olds are all a bit ghastly, and she didn't exactly have the best parents to give her a start in life.
Lizzie is unrealistic - being really rude to the richest, swankiest man in the land when you've got little to offer, and still marrying him? Not very likely!