If you don't like this type of post (fancast), please just skip it instead of sending hate my way!

A few thoughts: I made some casting swaps that I think would have been advantageous. 

Going in order: personally, I’m not a fan of Ed Westwick; after reading the books, I felt Chuck should have been played by a more handsome actor, and for me, Dave Franco has the right looks and vibe for the role. 

I’ve mentioned AnnaSophia Robb as Jenny before; she captures the Season 1 Jenny vibe perfectly, and looking at her now, you can see exactly what that version of Jenny might have grown into. Anna is a fantastic actress who would have done an amazing job and without having to give up acting, we might have even gotten a Jenny spin-off starring her, with a The Carrie Diaries kind of vibe (if you know, you know). 

I cast Reese as Alison because she bears a slight resemblance to AnnaSophia (in fact, Anna has played a young Reese before, I'll post photos of them together in the comments!), and I wish Alison had been more involved in the show. 

Lucas Till makes more sense to me as Eric, he captures the character's essence and looks more like a brother to Serena/Blake. However, I didn't want to leave Connor out, so I cast him as Jonathan a smaller role, since he leaves the show later anyway. 

I didn't rule out Taylor Momsen, either. I could see her as Agnes, but a well-developed Agnes, not the diabolical one who drugged Jenny. I imagine Taylor bringing her to life as a lost young model trying to find her place in the world, eventually starting a rock band and choosing a music career (they could have promoted TPR through Agnes within the show, plus her style naturally mirrors Taylor's real-life look). It would have been a smaller role that didn't tie Taylor down, allowing her to focus on her career the way she wanted to back then. 

As for Alexander as Damien, he definitely gives off "bad boy" vibes, but he would have been the right age to be a romantic match for Jenny (or even part of a somewhat toxic love triangle involving him, Jenny, and Agnes, had the writers been bold enough).  

Casting Kelly Rowan as Carol playing Kelly Rutherford’s sister no need explanation, watching The O.C and seeing Kirsten on screen is like seeing a lost sister of Lily. 

I don't have much to say about Sara Paxton and Jennifer Lawrence, I just think they fit the roles well. Sara, especially, she could easily pass as Kelly’s daughter. 

The book characters I added belong to Jenny’s circle; having them in the show would have meant Jenny "lost her way" less and didn't try so hard to fit in with the older crowd. Seeing Jenny develop relationships with Agnes, Elise, Tyler, Leo, and even Damien would have been better for her character than trying to fit in with Blair, Serena, and Nate, who already had their own established dynamic without her. Leaving them out of the show was definitely a TERRIBLE creative decision. As for "Valley Girls," I imagined we could have had a few special episodes focusing on Lily’s past instead of a full spin-off series. I chose the actors based on appearance, James as young Bart was a choice I made simply because I cast his younger brother as Chuck. Casting Mischa as Carol would create another parallel between Marissa and Kirsten from The O.C, and I can totally picture Mischa playing a fed-up rich girl who leaves that shallow world behind to pursue a filmmaking career in Los Angeles, why does that sound so much like Mischa Barton to me? 

Sophia Bush as Eleanor would be interesting, given how often people compare Brooke Davis to Blair, though it would have been difficult since she was on One Tree Hill at the time. I wouldn't say it was impossible, in my idea, it would only be for a few episodes, she’d be more of a guest character (since Eleanor doesn't seem to have much involvement in Lily’s backstory). Anyway, guys, those are my thoughts. 

As for the actors I kept, I really have no complaints; they seem born for the roles. I just wish they were better developed (which is a general flaw of the show); I also wish Nate had interesting storylines and that Vanessa had the dark style of her book counterpart. But in terms of casting, I wouldn't change the ones I kept.

Again: don't hate me! It’s just a silly, fun post about a show that ended years ago.

The ideal cast for OG GOSSIP GIRL, in my opinion!