Lol, as of my vote, each sister has a 25% rating - except Lisa, she's dead at 0%.
I'm going to go with Lucy, and not because she's one of my favorite siblings, but because I feel like she'd be less of a headache to babysit for: the twins and their antics would be chaotic, Lisa's capable of doing anything that could result in some personal and/or property damage, Lily - being a baby - would probably cry a lot . . . but Lucy, she'd probably keep to herself, so I wouldn't have to worry about making sure she doesn't get into any kind of trouble . . . unless she decides to conjure up demons or something.