For my money, we really enjoy The Pinery Provincial Park. Next is Algonquin at a close second.
At the Pinery you look out over Lake Huron at the breathtaking sunset and the blue water and look at the white powder sand and you could almost think you were in Acapulco. I am not kidding- it is THAT nice.
Most lake water looks grey or steel blue but these water are warm and blue- exceptional swimming.
I know National Geographic List lake Huron as and The Pinery /Grand Ben/Bayfield as having the worlds best sunsets.
The staff is excellent and knowledgeable with lots of trials- some wheelchair/stroller accessible. Lots of guided hikes. Bike trails and more. I winner in every way.
Downside is it is REALLY hard to get in.
Another very nice park if you can get into it is Killbear. You pretty much have to book in spring.
Sandbanks also a good one but I have not been in a few years.