North Dakota vs South Dakota from Detroit to Yellowstone?

ND is one of the few states I have not been in. other than as a bucket list item, I would go a little further south.
bumpy

Some places we have enjoyed when crossing North Dakota on I94:

Fort Abraham Lincoln - George Armstrong Custer's last posting before he led the 7th Cavalry to the battle of the Little Bighorn. Several buildings have been reconstructed, including the house he lived in. There is a campground with electric hookups there.

Theodore Roosevelt National Park - The main entrance to the Park is near Medora, but a stop at the Painted Canyon Visitor Center, which you would pass first when heading west, is well worthwhile. Medora itself is also an interesting stop.

Pompeys Pillar National Monument - is adjacent to I94 in Montana. Captain William Clark of the Lewis and Clark expedition carved his name and date into the stone. Nice visitor center there as well.

If you would like to enter Yellowstone via the east entrance from Cody, take route 212 south from Laurel to route 310 to route 72/120 to Cody. An easy drive.

Not much in ND. In SD, there is Rushmore, Badlands, and of course, Wall Drug.

Ditto on the sites in North Dakota. Teddy Roosevelt National Park is excellent.

While there aren't many big sites in ND, there is a lot to see if you keep an eye open. Plus, it will be a little bit cooler up that way. Since you've already seen the big stuff in SD, why not? After all, isn't traveling about seeing all this country has to offer, not just the highlights?

We had a trip planned for this month that was three weeks and ND was the destination because it's the one state west of the Mississippi we haven't seen. Trip was postponed due to work, but I still have my notes because one day, we will get there.

In addition to the ND places mentioned by CloudDriver, add Fort Union which is an old restored trading post near the confluence of the Yellowstone River where it joins the Missouri, and add a visit to Mandan on the Missouri River just west of Bismarck where Lewis & Clark spent the winter of 1804-05 while on their westward journey. North Dakota is a great state to visit, the highways are in excellent condition too! I'm a native South Dakotan and prefer to travel in ND over SD whenever making a trip eastward......and it's not so overloaded with tourists either.

Thank you for all of the suggestions. I think we will be going through North Dakota.

I traveled on US 12 across the USA on a motorcycle trip. 12 is the real world USA. It's a good 2 lane highway that widens to 4 in the busy areas. You won't make real good time, because there are lots of small town, but it's America in real life. I'd do it with our 42 ft toyhauler no problem.
Stop at small town USA and visit a museum.

See the next town ahead.

If you don't go thru S Dak. you will miss Devil's gulch, in Garretson.
bumpy

Last September we did the Mt. Rushmore/Badlands up to the ND Badlands (T. Roosevelt NP) loop and then back home with our TT. Loved it. Our opinion is the ND Badlands are more scenic than are the ones in SD.

My advice is go to the State of ND website and see what there is to visit there. Mandan where L&C wintered when heading west, etc. Good, smooth roads was my experience in that state. I was impressed. See something new.