Our favorite time to come to the area as a family is in August, right after most of the kids go back to school. The pool water and ocean are so comfortable, everything is open and not crowded, and there is very little traffic. We're from the north so our kids don't start school until after labor day. We're only coming there for one week this August (and we're going to be there the last week of June, too, to see what it's like at peak season), but in the future we'll come for 2 weeks (maybe more) in August.
Keep in mind that some places along 30A are going to have more traffic than other areas. We pretty much stay at the pool, porch, and beach so we don't have to deal with traffic too much (grocery shopping). When we go out to eat, we do that early (e.g., 11:45 for lunch; 4:45 for dinner) because we have children so they actually prefer to eat early.
The trade-off you make is this: At the busier beaches/roads, you have restaurants, shops, etc. within walking distance but there will be more crowds and traffic because of the restaurants, shops, etc. At the less busy beaches/roads you have fewer, if any restaurants/shops/etc., within walking distance and you have fewer crowds and traffic.
Hope this is helpful.
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