Flannel is one of those fabrics that while it makes a great quilt it stretches a lot especially on the bias. Most flannel is cotton of a very loose weave. There are different grades of flannel, some looser and stretchier than others. Usually I'm not about fabric weave unless it's really horrid, but with flannel I always purchase the "Quilters Flannel" it seems to be the tightest woven.
Are you asking what type of fabric is best to use when quilting, the weave is how the fabric is actually assembled. There are no hard and fast rules about the fabrics that you must use for quilting. Most quilting fabrics are cotton. Brand name fabrics like Moda, Bernatex, and the others are cotton. The thing that I think is most important is when assembling the fabrics for your quilt try to make sure that all of the fabrics are the same weight. It makes for a more even feeling and looking quilt that lays right.