I recommend using plain whole milk Greek yogurt for this recipe. It's what keeps these muffins moist and adds some protein. My go-to yogurt brands are Fage 5% plain Greek yogurt and Siggi's plain whole milk yogurt. 2% Greek yogurt will also work, but I don't recommend using non-fat Greek yogurt as it won't add as much moisture to the muffins and it sometimes has fillers which could change the consistency.