I suggest you first bring your family to Hangzhou for a visit, stay for a bit to see if you all adapt well, and then decide. If you have children, you'll also need to factor in education.
It's hard to compare; one is a provincial capital, and the other is a prefecture-level city. But I've always loved the saying, 'Above there is heaven, below there are Suzhou and Hangzhou.' I'm very fond of both places.
