I've lived in Michigan my whole life but far and away, my heart belongs to Pinery Provincial Park, Grand Bend, Ontario, Canada. Out of my 37 yrs., I have probably camped there 24 summers and my father many yrs. with his parents and siblings before I was ever thought of.
It is huge, gorgeously forested, with beaches (and 1 campground, Dunes) on Lake Huron. There is an awesome river to canoe on and plenty of peaceful trails to hike. We have mostly tent camped in the "Riverside" part which is closest to the camp store and, yes, on the river (if your in the full service section for trailers, then you're elbow to elbow). As we all get older, time between camping trips get further apart, this year we are going for the first time in 3 yrs. That is partly due to how packed it is, you have to make reservations almost 6 mths. in advance now. We will always love Pinery and go back though.
About four years ago our family discovered the most perfect lake in the middle of the eastern Upper Peninsula of MI. It's maybe about a 20-30 acre, perfectly oval lake, surrounded by pine forest with NO developement, just the campground. You have to drive on a seasonal dirt road for about 5 min. before you get to the campground, which only has about 20 campsites (1st come, 1st serve), outhouses and water pumps. Absolute heaven. Peace, serenity and beautiful nature. Forgive me for not giving out the name of this haven.
Unfortunately, with the recent years gas prices and the U.P. wildfires, we haven't been able to get back yet. Major bummer.
As for National Parks: Of what I've been to, Yellowstone hands-down. Toss up between Zion or Bryce canyons for second (Grand Canyon doesn't count in my eye's, it's a "world" park/wonder).