Ultrasounds are better for women under 35, because younger breast tissue is denser and harder to see abnormalities on a mammogram.

For the general population (women who have no family history of breast cancer), women are encouraged to get a baseline (first) mammogram at age 35. But definitely point out any lumps or sudden changes in the look of your breast (dimpling, etc.) to your OB/GYN as soon as possible.

I speak from experience. My cancer was found on a mammogram at age 33 (I am the fourth generation in my family to have breast cancer), but I'm 35 now and am healthy, thanks to that mammogram and ultrasound.