What is better, to have more time during sono with tech or brief time with ob expert?

Ultrasound. They serve different functions. The tech is trained to obtain and record ultrasound images. Ob expert specializes in interpreting these images to reach a conclusion. Either way, I wish you get your answers.
It depends. The quality of any imaging test is only as good as the person reading it and the person performing it. Get your ultrasound at a place that does a lot of them on a regular basis and where it is read by a radiologist or obstetrician who specializes in OB ultrasounds. This is usually the case at a woman's hospital or major university, but not true at imaging centers.