I personally prefer a fluffy poly batt with less quilting than is currently popular. I would not double warm and natural over an entire project because it would be very heavy, but I have doubled it to make appliques raise and such. The weight is both an issue if you are quilting it on a domestic machine, and the weight of the finished blanket itself.
There are times that I do want to use warm and natural because that will produce the finished product I want, but most times... I go fluffier. I have a top I just completed that I'm going to have as a summer quilt and I'll use a really thin poly batt in that one.