Somewhere between Peyton & Haley though.
Peyton because "best friend who sleeps with best friend's boyfriend" and Haley because of "nice girl"...sorta.

if you are going to use the "I slept with my best friend's boyfriend" you should compare Serena with Brooke and not Peyton because Brooke is the one that slept with Nathan while he was dating Peyton. P. Sawyer is more like " I fell in love with my best friend's boyfriend" and in GG that's Chuck.

anyways, I think Serena is more like Brooke because both were sluts and party girls and very popular at their school and also out of it, in their town/city. Also both of them changes and grew up becoming better persons.

Oh okay, well sorry. But that's not what I meant - yeah, she may have been in love with him but she still slept with her best friend's boyfriend. That was my point :P

actually she didnt, Ldeyton slept together in season 4 when Brucas were more than over, but whatever....we have diferent opionions about it lol

I don't think Serena is like Peyton at ALL (they're almost opposites =|) except for the cheating thing...but maybe thats my bias talking since I love S & I'm not a big P.Sawyer fan.

i think Peyton.

or Peyton i don't know

I always thought she was a mix of Haley/Petyon/Brooke. She's sweet like Haley, she used to be exactly like Brooke, she still is a little bit, and she has some stuff that is similar to Peyton, like her deep personality.

EDIT: BTW, sleeping with their best friends' boyfriends doesn't make them similar in my eyes. They both made mistakes, but does that mean that they are similar people with the same types of personalities? Personally, I'm really glad that Serena slept with Nate. Without that, we wouldn't have the potential magic that is SereNate. :)

more of a mix between brooke and peyton.