I've been in big and small cities all over the place and I still think Lexington and Cincinnati are two of the best cities I've seen (although Cincinnati can get dicey if you live in the wrong part of it. ). Lexington isn't for those that like hustle and bustle, though. It's for someone looking for the slow pace of a charming southern town to raise their kids.
Fort Collins, CO. is also a nice place to raise the kids. They have a park every block, I think. It's not as beautiful as some cities I've been to, but its a great place to have your family.
Chicago is my favorite "big" city. It has such a vibrant feel to it. There's something for everyone and I've really felt comfortable the times I've been there.