It depends on what you need it for. If you don't need the greater functionality of the 580 then the 430 will be fine. Compare the spec of the two against your needs and weight it up.
I have several of both but as a stand alone flash I always reach for the 580 first, just because its has slightly more power and functionality. That said, the 430 is a very good flash.
Its difficult to answer your Q' without knowing what funtionality you need.