We have stayed at both. I like the Platt river campground myself. This is a federal park so you are subject to the federal park fees. Nice area to explore and enjoy the lakes and dunes. Ludington is also a good spot more to do in the way of town type stuff.another choice in between is Orchard beach state park in Manastee. I like Manistee and the little shops etc.. You can wait untill July and the weather will most likely be warmer as well as the lake temps. you will also have fewer camping choices as you will be at the peak season. I have not experienced black flies in the areas where you are considering.
