Agree with everything backforgood says - it's the home from home aspect that drew me to a childminder more than a nursery. That and the idea of a little second family, with the other mindees and maybe the CM's children.
When we met our first CM, I barely asked any questions, I walked in and CM immediately asked for a cuddle with (4mo) DD and I had an overwhelming sense of "I like you, and I like your family". The little things they did were wonderful - occasionally during the school holidays DD would be the only mindee and they would go out on a family day trip and just take DD along like another member of the family. I was devastated when we had to make the decision to move to another CM.
I also wanted a CM to be more flexible than a nursery, which so far has turned out to be the case - as in, they have understood that with some families it's not as simple as needing care either 60 hours a week or every Tuesday and Wednesday, and we've been able to come to some compromise over our silly work shift patterns and their financial stability.
On a very practical note, someone who has good contacts with other CMs in the area so that there is a chance of finding emergency care if needed, and who tells you about their holidays in plenty of time so you can arrange your own cover.