Ralph prefers Xander because he doesn't have to put up with him as a crying baby, while Rozy is an ever present inconvenience, and Ralph, being a hedonistic, lazy, alcoholic, drug addicted, morbidly obese wigger who runs out of breath from walking a few yards, thinks every single thing that takes effort is unjust and evil.
That's it. Were their mothers swapped, Ralph would prefer Rozy.
Other than that, he hates children, he never wanted children, he stated so multiple times on the Killstream years ago, right up until Null's post about wanting a family, which drove him to produce two spite babies exclusively to epically own Josh and his broke dick.