I'm doing reviews for River Heights series. That's a Nancy Drew spinoff series; it mostly follows Nikki Masters and romance drama at her high school. Nancy occasionally appears as a background character.
Now that I've read "Sweet Valley High" books, I can see that this series is a VERY direct copy of Sweet Vally High. The main difference is that the two main characters, Brittany and Nikki, aren't twins. Other than that, Nikki acts a lot like Elizabeth and Brittany acts a lot like Jessica.
I like Brittany more than Jessica, because Jessica is 100% selfish and cruel, whereas Brittany often feels bad when she does nasty things. I like Elizabeth more than Nikki, because Nikki is pretty bland, whereas Elizabeth is...well, okay, she's bland, too. Oh well.