What determines your use of the type of DB framework/abstract?

Hey All, I'm guessing that the subject probably doesn't fit the question I'm asking here so I'll apologize in advance. Lately I've been getting in to how I can streamline my development after a bad experience with a contract. One of the areas I was looking at is when it would be appropriate to use certain DB frameworks? What I mean by frameworks is probably more like DB abstract, like Doctrine or ZF's native Zend_Db. I know this isn't a black and white explanation so I would like to know what influences your decision on using a DB abstract framework. Whether to use one or not and if so which one? Jamie