They both have value. Ultrasound is a good screen for some conditions like tumors or cysts. Biopsy ismore useful to confirm the suspicious diagnosis. So most patientss need both tests.
See below. A liver biopsy is an invasive procedure that carries more risk than a noninvasive ultrasound. If something can be answered by an us, us would probably be better. If you already have a known diagnosis of cirrhosis, lab works, us or ct or mr can be used to survey the liver periodically for tumor.