Which is a better diagnostic procedure a digital mammogram or sonogram?

Digital mammogram. For general screening, mammograms, while imperfect, remain the best tool and digital mammograms are better at "seeing through" breast tissue. A mammogram is more likely to miss cancers in women with dense breast tissue and young women. Ultrasound is most often used with mammogram either to help characterize abnormalities seen on mammogram or to aid in finding abnormalities in dense breast tissue.
It depends. Neither is inherently better than the other, they are complementary diagnostic studies, and one or another or both may be appropriate depending on the clinical situation. At your age, ultrasound is probably the initial imaging study of choice if you have a lump. In the screening setting, mammo is the standard of care, but the role of ultrasound is evolving, particularly in dense breasts.

Related Questions

For best detection which is best digital mammogram or sonogram?

Mammogram. Mammogram remains the first choice for breast cancer screening. There is a select group of patients for whom screening ultrasound and MRI breast will be added to supplement the mammogram.
Mammogram. A mammogram (preferably digital) is still the best screening imaging tool. Ultrasound is not currently used as a universal screening modality. However, it is an excellen adjunct test if there is a clinical, mammographic or MRI abnormality which needs further evaluation. In addition ultrasound is also very effective in targetting a lesion which may need a biopsy if it can be seen by ultrasound.
Mammo/US. Mammo is the standard of care for screening. Mammo is approximately 80% sensitive for detecting breast cancer. Sensitivity decreases in women with dense breasts, some say to as low as 40-50%. There is some data to support adding screening US as a supplement to mammography in women with dense breasts, which can detect an additional 3-5 cancers per 1000 patients. False positives a problem though.

For breast which is best digital mammogram or sonogram?

Depends, maybe both. A digital mammogram is the standard for mammograms. Sometimes an ultrasound may be added to get more information, especially if you have dense breast tissue. In younger women with dense breasts, a mammogram may no be done and then we go straight to ultrasound. A breast radiologist and breast surgeon will be able to make the appropriate recommendation for you.
Mammo vs sono. Mammography is still the screening standard of care for dense breasts. The sensitivity of mammography for detecting cancer (80% across the board) decreases in dense breasts, some studies show to 50% or lower. There is some data to suggest sonography performs better than mammo in dense breasts. Many are now performing both screening mammo and sono in dense breasts, it is an evolving situation.

If small calcifications show up on a digital mammogram and not on a breast sonogram. Should I be concerned?

Not yet. It's not that simple. You should be concerned only when your surgeon tells you to be concerned. There is not enough information in your story to make a decision like that.
Calcifications. Small calcifications may be difficult or impossible to visualize on ultrasound, while being relatively easy to see on the mammogram. The fact that the calcifications are not seen on US doesn't make them any more or less suspicious. Speak to your doctor about the next steps to take.