I think I go through cycles, honestly. It used to be that Speed ate my brain all the time, but that slowed down a bit for Hippie and then Narcissus when I picked him up. I think it mostly depends on how I'm feeling. If I'm extremely happy, Speed gets the most attention, though he's my oldest (excluding Hollywood, who was my first but was dropped) and will always have a special bouncy place in my heart. Hippie's probably the most like me, personality wise and a lot of things with her/him come easily. Now that Lilith has kids around, I have more of an opportunity to flesh her out, and the same with Narcissus now that he has a kid on the way. As for Saleos, I see him as a more of a minor character in my head, if only because he generally sticks to interacting with his family and Nergal.
This was harder than I thought XD I think, at the moment, I'm at an odd place where they're all equal, but usually there's a front runner demanding my attention more than the others.