Here's a tale of two dresses, both McCall's 5752 (the self-proclaimed "perfect knit dress"). I'll spare you the Dickens quote, as you're probably already thinking it to yourself (ha!). If I had read the book I could pepper this post with all sorts of literary allusions. Instead I'll settle for Patty Duke Show references. (I watched a LOT of those reruns.)
I recruited my identical cousin to help illustrate how fabric selection can make or break a garment. The dress on the left was my practice version, made from a jersey advertising banner rescued from a Dumpster. This fabric has a beautiful drape, great recovery, and feels as cozy as pajamas.
The dress on the right is from a visually interesting, but utterly awful, clearance rack knit. (What you can't see in these photos are rows and rows of subtle light brown stripes.) It doesn't hold its shape, hangs like a sack, and clings like a sock out of the dryer. The fit was so loose that I slit the dress up the back and took it in by several inches. And yet I still look like a Jedi reject.
Let this be a lesson (most of all to me, who keeps repeating this mistake): not all knits are identical. Get to know a knit fabric's personality before you invite it to live with you.