I prefer Kona solids. They are a tighter weave, and comes in a lot of colors. Natural would probably be closest to a muslin look.
You can buy it at Joanne's, Hancocks, and Hobby Lobby. Hobby Lobby usually has it on sale.
I was watching Eleanor Burns Egg Money Quilts video and she talked about using Kona Solids so that's where I learned about them.