In later August, many families will be heading back to home state to get kids ready for school . . . but summer is a busy time over all. I don't think it would matter that much - just make sure you book your lodging & car rental early. :)
All your proposed dates are during high season. I don't think either will be significantly different. If you could move your trip to early September after Labor Day (9/1) the crowds will be less.
The weather and ocean conditions would be similar. You might find fewer families with school-age children in late August.
I would also take the late August dates, most schools in California now start in late August with will cut down on the crowds during this time. (California visitors make up a huge percentage of visitors to Hawaii)
I would take the later dates, too. In addition to mainland visitors not being as thick, our schools here start up in early August.
I would pick late August also. Avoid the July 4th crowd.
Toss up! If at all possible, I would delay into September or October or early November.
Note that the first set of dates includes July 4th.
Are you spending both weeks on Oahu? Why not split your nights and see another Island?
BLBL - they are seeing Maui & Kauai - she did mention that in the post. :)
We are limited by school vacations, school here starts after Labor Day.
Sorry, Coalminer ... I have "Oahu Brain."