I have made a lot of Granny Square afghans with Plymouth Encore Worsted, but I only used one strand of yarn. So for this sample, I decided to use two strands and a larger hook (an N 15/10mm). The square worked up really fast, and it still felt as soft and as cuddly as one strand of Encore Worsted. Using two strands is a great way to use up odd colors of stash to make a quick baby or full size afghan! (See my afghan pattern, Gramma & Grandbabies, in 50 Sensational Crochet Afghans and Throws, edited by Bobbie Matela).
This next swatch is Noro Kureyon, a yarn that is not often used for Granny Squares. I love how it self-stripes, though, and I wanted to see how it would look in Granny Squares. One neat thing about self-striping yarn when you work it in rounds. If the number of rounds you work is small enough, each separate piece you make will look different, because the colors are in different places, or they are not repeated in the next piece. This is what happened when I made more Granny Squares out of Kureyon, and you can see a small portion of the other two squares I made on the sides of the middle square. Try it for yourself. One skein of self-striping yarn is all you need, and I recommend one like Kureyon (or Plymouth Bocu). Make Granny Squares of only 3 or 4 rounds. Make at least 3 of them, and see what you get. They all look like they came from different skeins! It's a great way to get lots of color into a design!