Beets are typically in-season late summer to early fall. They should be firm to the touch, and not have bruises, cuts, or soft spots. Smaller beets tend to be sweeter and more tender, while large beets tend to taste more earthy. I try to select beets about the size of my fist for perfect taste and texture. Bonus if the store is selling them with the green tops still attached, you can tell they are fresh because the leaves have not dried out or turned brown.