Is 6week or 12week ultrasound more accurate for due date?

Justine

According to the measurements at my 6 1/2week ultrasound I would be 11 weeks and 5 days today.However,today I had an ultrasound and am measuring 12 weeks 4 days.Which is more accurate?🧐According to the first day of my last period I would be 12weeks and 1 day