Anyone who has read past Twilight's New Moon has probably thought about this at one point or another. In fact, I do believe that it is one of the most compelling points of debate among Twilight fans, considering that Twilight is essentially a romance novel.
Edward and Bella vs. Jacob and Bella. The debate sounds very shallow, more like tweens debating over the cutest guy in the Jonas Brothers Band, but with respect to the story's premise, the choice between the two is more than just a choice between the beautiful, perfect vampire and the passionate, kick-ass werewolf - it is a choice between immortality and humanity.
The relationship between Bella and Edward is doomed to failure if the Cullen boy doesn't choose to transform Swan at an age when they would look like husband and wife, rather than grandma and grandson. However, that would mean that Bella would have to give up the latter portion of her normal lifetime and live an eternal life of darkness and isolation. Bella is stupid enough (forgive me, die-hard Bella fans, I like Bella too but I believe that she is being unreasonable) to cast away all of these things, implying that humanity is overrated anyway. She doesn't realize how sad her life will be if she never sees her father, mother, and Jacob again. I believe that her concept of love is still very immature - she imbibes the idea that love is just about the guy and the girl; nothing else comes close in importance. And it is this aspect why I am not a fan of the Bella and Edward ship.
On the other hand, we have Bella and Jacob. Jacob isn't perfect. He's not good with words - he ends up openly showing his bitterness when Bella chooses Edward over him. He calls the vampires bloodsuckers even though he knows Bella is very amiable with the Cullens. As a werewolf, it is his innate behavior to have a short temper. Thing is, Bella is head over heels in love with Edward that he considers Jacob only because Edward left her. She doesn't deny that she loves Jacob - it is impossible not to. Jacob knows her inside out, even without any vampire mind-reading skills needed and he is madly in love with her. However, Bella seems to be more entranced by Edward because of the allure and mystery that revolves around the life of a vampire. I believe that choosing Jacob will be a mature step for Bella - a point in her life when she realizes there is so much more to life than just the love between man and woman. With Jacob, she can enjoy all the things a human can. With Jacob, life is not perfect, but it is real and whole.
To be political, I would agree that Bella's relationship between Edward and Jacob are equally appealing in that both men are always on edge with their instincts - they are both struggling to put a bridle on their true nature in order to be with her. Edward has to battle with his bloodlust. Jacob has to battle with his phase-causing temper. I just lean more towards the werewolf because of my reasons above. If you are an avid Edward/Bella fan, please do not flame me ^^