This is totally what you think, not what the book says. Do YOU think Bella should stay human or become vampire?

I think Bella has no other choice than to become a vampire, if she wants to be with Edward forever.  In a normal human existence, a married couple will grow old together over a period of years, but Bella will never have that because of Edward's vampire status.  The alternative to becoming a vampire is to grow old and eventually look like Edward's grandmother; although Edward says he will always want to be with Bella no matter what she looks like, this is not an alternative Bella wishes to contemplate, much less experience.  Of course, Edward resists the idea of Bella changing over because he doesn't want to deny her the world of experiences she will have as a human being; he also recognizes that once Bella has changed, it is irrevocable.  However, for Bella, this step into immortality is not an option, but something she needs to do to be with Edward forever as an equal-opportunity vampire.