Trust the 6 w 3 d ultrasound over the later one(s). Babies do grow at different rates.
My doctors with both of my kids gave me u/s dates that were sooner than the lmp dates. I ended up having my son waaay after the u/s date on the 20th (I had to be induced), the u/s date was the 8th and the lmp date was the 10th.
The u/s date for my daughter was the 3rd, the lmp date was the 8th and I was sure of the conception date. She was born on the 8th.
I agree, go with the earlier one. All babies grow at different rates. It's not uncommon for an ultrasound to be off a week or so either way. Besides, due date calculation is not an exact science. I've always gone by my first ultrasound date.
I had my 12w ultrasound last week. It confirmed that the second ultrasound date was accurate.