I think both weeks will be about the same. Since the 4th is on a Saturday, many people will be off on the 3rd and will go the week before to take advantage of the 1 day work holiday if they go for a week. In contrast, we always try to go for a few days longer than a week and we'll start our trip on the 3rd and go through the following week - basically using the Friday off as an "extra" vacation day this year.
We went the week after the 4th last year (basically same situation with the 4th holiday being on Friday), and thought that the crowds weren't too bad. Keep in mind that we always go at crowded times though (XMAS 3 times), so it's all relative. And since we're frequent visitors we know how to tour the parks, and we're fine with missing out on a few things "this trip" because we know we've done them before and we know we'll be back again soon! This would be different for someone who was taking a "one-time" trip.