What is more accurate? transvaginal us, or pelvic us?

Depends: both types of pelvic ultrasound approaches are useful and which is better depends on what part of the pelvis is to be examined and often the body size and shape of the patient. Many clinics do both if they are indicated based on the clinical question requested by the ordering doctor.

Trans vaginal: Transvaginal ultrasound is always more accurate then abdominal ultrasound as the transducer is closer to the pelvic structures.