K.P.
Robin is so right in saying that their personality will flip. My Boy/Girl twins (11 months) did this too. My boy was so laid back and my girl was super super needy and whiney....and now...total opposite. My little man needs all the attention while baby girl is content playing on her own.
So don't feel too guilty spending more time with one vs. the other. Her time will come when she needs mommy more then sister does:)
Take care and congrats on your little twin ladies!