I'll also bar Sakura since he kind of already knew she lived with them before he came back and she was gone.
Itachi would choose...probably Kitty. She knows him and Sasuke and puts up with their oddness and he wouldn't try to put her into a mother role since Itachi kind of killed his mom. Not pseudo-family since he doesn't have a good track record there, but he also thinks Kitty would know how to keep to herself enough not to question why he doesn't sleep much and can spend most of his nights staring at nothing.
Kitty decides Itachi has to learn about the birds and the bees. How would she broach the subject and how would she take finding out Itachi's been there done that and didn't want the t-shirt?