I use Hobbs Heirloom Wool for just about everything. It machines excellently, has great drape, and is, as Shelly advises, cool in the summer and warm in the winter. It has the loft of some poly blends but none of the hassles. I won't quilt something for someone else if they want poly batting, life is too short, to have to fight that stuff.
I purchase batting by the roll. It seems like a lot to purchase but it doesn't go bad and you get great prices.