i want to make some point clear

Never read the book but I loved the movie.

Which would you say is the better story?

Well for me it seems with all these differences the film has a better, more complex story. (I haven't read the book, I'm founding my opinion on the OP's statements.)
If Rip was kind of a lost case from the start and Jack never made that disgusting gesture about the money without even trying to talk to Rip first - well that makes the whole story much more one-dimensional, that way it's only about how stupid laws can be sometimes, and morally, emotionally it makes clear that the adoptive parents should keep Joey whitout a doubt.

The very thing that made this film special to me, different, more than other similar themed films was that at first both couple seemed to have a chance in being good parents. For the viewer it was much more challanging to think about which one of them would have the right to keep Joey than to just simply pulling for 'the good guys' and hope that the big bad Rip will loose.
In the film Rip really wanted to stick to his improvements, wanted to be a changed man, he truly wanted to be a good husband and father. He did not succeed for sure, but not because he was already lost the fight before he had started it.
In the way the book tells the story according to the OP, it's also hard to understand Wendy for sticking to him, she would be just like any stereotype abused woman who can't break the circle.
In the film I actually expected these reactions, like Rip to loose it when he realised what Wendy did, terrify Joey the first moment they met etc., and when these did not happen I felt emphaty for Rip. He was a weak, deeply damaged man, but he did try to be better, and in the end he did at least what he could for Joey, let him be with people who can be as good parents as he wished to be. I hate woman-beaters but in this case I kinda could understand why Wendy felt that there's some good deep inside him.