You can use other flavors of yogurt as well, though plain and vanilla work best
Any kind of berry would work, but recommend strawberries, blueberries, or raspberries. Blackberries tend to be seedier and harder.
Butter is best when softened to room temperature. But if in a hurry, microwave in a small bowl 15 seconds at a time to make sure it doesn’t over heat and boil over.
Double recipe to make a 8in loaf or 12 regular sized muffins. Also increase the bake time to 50 minutes for loaf and 30 min for muffins.