@electricsky: Haha, yes, that clears it up, but it read even funnier before.
Anyway, I may be able to give you some insight into your actual question. I have a two-year-old female cat (Ilsa) and 2 female twin kittens (Nicolette and Alexandria). Ilsa is far more affectionate with Nicolette than with Alexandria, and it just seems to be because their personalities are more similar. Alex is sweet and demure. Ilsa plays with her sometimes, but usually Alex takes it for about ten seconds and then moves along because Ilsa is a bit too rough for her tastes. Nicki, on the other hand, looks up to Ilsa as a role model, as they are both feisty and aggressive. Nicki can take any amount of play-fighting and loves cuddling/fighting with Ilsa.
In the case of my girls, relationships seem strongly driven by personality characteristics. (Nicki and Alex also have a strong relationship with each other, as they are the same size and genetically related. And were born and survived together in a dumpster.)