Is it harder to decide who gets what gift if they are into similar things?

My girls are 18 months apart, and play with similar toys for the most part. I'm done Christmas shopping for them (minus LO1's main gift) I'm trying to decide how to divide it up. I would love to just put both of their names on it but that's not fair either.

If your kids are into the same things, and you buy gifts that they are both into,, how do you decide who gets what?