O day is more accurate. I would think you are 3 weeks, 3 days pregnant as that equals 10dpo. Your EDD being February 14.
The Dr. will go by LMP at first. But, they'll eventually change it anyways. I went by O day because I'd rather just keep the same due date and not be put back later.
Based on LMP I would be due January 19. But, based on O I'm due January 26.
It really doesn't matter what you go with. If you are measuring behind, just remember your O'd later.