Well, I am thinking that it would depend on what you are buying it for. In the back of your mind you are thinking ?Would this be a feature fabric in the design, or a border print, or just a fabric you think might go well in a setting with other fabrics you have on hand, like a blender.
Usually a 2 yard cut is good. But if you are thinking you love it , three. If you are liking it, but not sure if you will ever use it .. a fat quarter might be enough. Hard to say really. It depends on how much I love it. And if I think it would make a good backing then I buy enough for that. I carry a little card with me that calculates the size of quilt backings. 108 inches is my queen size measurement.
Then I also sew clothing and purses, totes and hot pads, ect ect. So cutsie kitchen crafts a couple yards. See where I am going here?
It is hard to tell you what I would do. I have something in mind when I buy it.