That's a hard decision. I guess I fall on the other side of the argument. If you already have a good PI you know you would like to work with and is a good mentor, that is worth quite a lot based on my different lab experiences. Some of the most successful researchers I know received multiple degrees from the same university (BS+PHD+MD or DVM). But this is coming from someone who wishes they could head back to a previously attended university.
Either way you will be attending excellent programs, so you only have 2 good choices!