I love mulberries. They're nostalgic for me because I grew up picking mulberries. They're so sweet and delicious, but I've never seen any for sale! (Typing this as i eat some blackberries!)
There are mulberry trees in our neighborhood, and now Charlie and Olive love mulberries too! We pick them every time we pass by one in particular (the owner told us we could).
Second runner up would be strawberries.
What is your favorite berry?