The box came with two brush heads, one large and one small. I've only tried the tiny one. I have tiny teeth. They seem to work well together. Why mess with success.
Best investment I've made in a long time. My teeth were noticably whiter within a few days. The toothbrush action is much milder than the older electric that I used to use; cleans without gum irritation. The water pik function is so invigorating without hurting my gums. I've recommended this to family and friends.