i always like to go in may and early june to avoid the crowds and september and october is nice too. there are plenty of campgrounds on the island, so you can normally get a site even in july and august. there are 2 nat'l park campgrounds, one at blackwoods(reservations) and one at seawall, which is 1st come 1st serve. Seawall is on the quiet western side of the island and it has a natural seawall of rocks that you can walk on and watch the tide come in. I wouldn't go in july and august and look for affordable housing/hotels, it will be busy and expensive then. if anyone is taking route 1 up to the island, i would also suggest a stop in camden, which is where i live. it is about an hour and a half from bar harbor, and we have about 5 different hikes w/ ocean views in the camden hills area, a lot like acadia. there is also the camden hills park off rte one to camp at, which is a nice campground.