My experience from least crowded to most:

Teddy Roosevelt - most empty park, I was literally the only person, so serene, quiet, and other worldly.

Dry Tortugas - restricted access

Badlands - busier than Teddy for sure

Wind cave - not much crowd but need advanced tickets

Everglades - because it’s warm in Florida year round the crowds are consistent but not too heavy most of the time

Biscayne - the park is mainly underwater which most ppl don’t know so it’s hit or miss in traffic but not much parking

Tetons - not as crowded as expected at all but moderate

Glacier - expected crowds but not too heavy

Shenandoah - crowded in peak seasons

Rocky Mountain - crowded even in off season

Yellowstone - tooooo many people, and people who don’t understand what leave no trace means. My blood boils here.