I don't necessarily think the designers you mentioned have fabrics that are superior to others, but rather the name is what sells. I've bought them so that's just my experience. I buy on sale almost exclusively ( unless it's something I really want for my grandchildren
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One of my favorite fabrics is Art Gallery. They feel fantastic and are a joy to work with. I have some sprinkled in my stash but again, I get them on sale. Not cheap but heavenly to work with.