Just my .02, but maybe it will help. I've sorta figured out which fabrics to buy by brand. Walmart has their own brand - cheap price, cheap fabric, usually 2.44 or less per yard. They also carry AE Nathan - low to mediocre fabric, usually 2.44/yd; Cranston VIP - mediocre, but better than AE Nathan, usually priced at 4.44/yd; Fabric Traditions - better than AE Nathan and VIP - usually priced at 3.44/yd.
Joann's varies quite a bit, but most name brand fabric is safe. The VIP fabric varies there and I've even started asking them to tear a piece for me because it is off grain more than not off grain, especially prints with squares. Last time I asked them to do that, it was almost 2" off grain. I'm tired of getting it home and find it wayyyy off grain. Besides, it's 75 miles to the nearest JoAnn's for me. Hancock - main fabric is Absolute Cotton and it varies a lot in quality, but it's on the mediocre to ok range. The novelty cottons tend to be slightly better and they carry a few name brand fabrics that are rarely on sale, but at least decent quality. Quilt shops - I trust their fabric. Mary Jo's in Gastonia NC is totally trustworthy and they carry mostly name brand fabrics, but not the same ones as the quilt shops. OK...that's my .02. I can't afford $8-10/yd so I have to be thrifty but I hate it when I get the fabric home and it's off grain and/or thin - arghhh.