I guess that may be the difference, those who don't get out and explore and those who do. We found Badlands to be moderately interesting and well worth a few days of hiking. And the surrounding area is worth exploring too, Wall Drugs and at the time the Minuteman NM which was doing tours of one missile silo. I've heard that was stopped and don't understand the logic behind that. W/o the tour the NM is worth a 20 minute stop at most. There is also a National Grasslands and a Homestead NHS area.
The Black Hills has the two caves which we've been to. They are worth a visit but compared to the major caves: Mammoth and Carlsbad don't amount to a lot. Rushmore we were underwhelmed by, it will appear a LOT smaller than you are imagining right now, it will be packed with people, and the parking is an expensive PITA. They charge for parking even if you have a park pass BTW.
Crazy horse amounts to even less than Rushmore and was expensive on top of that.
Rapid City was of interest to us since they have a major mineral museum on the college campus and we are rockhounds.
But this all varies depending on what is your major interest. Lots of people really like Rushmore for example. But spending a week or more exploring the Black Hills makes no sense to us, but if you like Dollyworld it may be your spot.
Arctic Fox 25Y Travel Trailer
2018 RAM 2500 6.7L 4WD shortbed
Straightline dual cam hitch
400W Solar with Victron controller
Superbumper