I would go with scan date - more accurate.
Not only that, my due date with the scan was 1st Feb although my dates were more 28th Jan. Poppy arrived on 14th Feb!
There is nothing more disappointing than your due date coming and passing with no baby. As a hospital will allow you to go 10 -14 days over I wish I had 14th in my mind anyway as it's horrible horrible horrible going over.
By having an earlier due date in your mind doesn't mean a baby will arrive any sooner....no matter how much you wish it to!
