Hexies are my go-to portable project whenever I walk out the door and know I will be sitting and waiting for something. Even if I don't have a specific project in mind, I have a small sewing case ready with all the essentials to just pick up and go. My largest (king-size, first pic below) project used 1½" hexies and is reversible. The smallest used ¼" hexagons (second pic) and is a design by Jaynette Huff. I bought her book for this quilt alone.
My preference is to EPP with freezer paper, and my favorite size hexie is ¾" and I have made tons of projects with this size. I especially like to make table runners with this method, like the scrappy one below, that uses tons of reds and greens (third pic, my own design).