Best Breed of Dog

I’m sure a lot of you are dog owners and dog lovers. My 3 year old has been begging my husband and I for a puppy for the past couple of weeks. I’m very skeptical because we had to give away our 6 year old Australian Shepherd/Sheltie mix. She became very aggressive towards children, even babies. It was one of the hardest things I’ve ever had to do and do not want to go through that again. What is the best breed of dog for a household with small children?