If your only goal is biglaw and you don't care where you live, I'd say Penn. Philly isn't that expensive to live in, from what I've been told, and you've got the most money. All will likely do you well to get biglaw.
However, I'd definitely visit. The numbers are so close to each other that, if you went and liked one school over another, go to that one. Most will likely match (or come close) to matching Penn. I'm not sure about Chicago, but I think Michigan would if you really ended up wanting to be here after visiting.
You can't really make a bad choice here.