If you have 40 quarters of SS credits, then you can file I-864W, and I-864 is not needed from the petitioner. In that case, whether she's moving out doesn't matter as your income doesn't needed to be added to her household income, since the petitioner's household income doesn't matter. So there isn't really a difference between the two. Your daughter petitioning you would probably be simpler, as your wife's petition would need to provide evidence of a bona fide marital relationship, whereas there isn't much question about the relationship to your daughter.