I think that Shakespeare portrays her as a character somewhat in the middle of victim and predator. One could call her a victim in that Shakespeare's Cleopatra truly cares for Antony and believes at the beginning that they will have a future together.
However, it cannot be denied, even in Shakespeare's version of history, that Cleopatra was a savvy politician. She longed for attention and power and began with Julius Caesar in obtaining both. While it seems like her relationship with Antony is more sincere, it is doubtful (as least from how Shakespeare characterizes her) that Cleopatra would have allowed herself to become romantically or politically attached to someone who could not benefit her own ambitions.
It is possible to be both. Think of Circe: a wicked woman, yet hopelessly in love. Her jealousy and black magic do not make her lovable, yet one has to pity her for loving to this extent.
Imagine Cleopatra as a feminist. She might want and desire love, but that doesn't mean it's the first priority to her. She puts her own needs and power-position ahead of her heart. IF true love is her soul's desire, wouldn't she have only one true love?
The best route for you to take would be to study the real Cleopatra, and then analyise that against Shakespeare's version of her. This will give you two depicitons of one person, allowing you your own opinion of her.
The link I've provided is a National Geographic video special on Cleopatra. Hope it helps. :)