Rapid City and Jackson Hole would be the two airports, assuming that there are airports in those locations. Casper is somewhat in between and might work as a starting point for a round trip.

You could spend a week just in The Black Hills. It would be a shame to miss The Badlands, Custer State Park, Wind Cave, Jewel Cave, Crazy Horse. I would strongly recommend the wild cave tour at both caves if you are slightly adventurous and fit.

2 days in Yellowstone is not nearly enough. You should spend 2 days just around Old Faithful Geyser Basin area.

You could do both areas but you are going to miss a huge huge huge amount of what both areas have to offer. We spent 5 days in Yellowstone a couple of years ago and that wasn't nearly enough. We are huge hikers and we didn't even do a single hike there.

If you do wind up attempting both, you should be able to fly into RAP and then I would fly out of either Jackson or Billings. Flying into or out of Billings makes it easy to drive The Beartooth HWY(which is a 1/2 to full day event and is considered by many do be the best drive in America-certainly does make about every Top 10 List)

I know you want to include everything, but sometimes it is far better to enjoy things and really experience it rather than just checking a bunch of things of a list. Plus, you are going to spend a lot of time traveling and that waste time seeing the sights. With 2 weeks you could do it, with 1 week its going to be super tough. I would pick Yellowstone if I had to pick one over the other. Make your Park Lodging Reservations ASAP. Have a great trip!!

If they fly into Jackson fairly early in the day, they could spend a little time there and then do a loop through Grand Teton in the late afternoon and early evening. The next morning they can head for Yellowstone and have more time there.

Lee Ann

gdible, you are really planning two vacation destinations but the trip is do-able. There is an airport in Cody, Wy., as well as Jackson,Wy. The problem with using the 'area' airports is that the cost is very high due to the extra flights from major hubs. As far as rental cars, to pick up a car in one small town and drop it off in another town is also very costly. That is the issues of wanting to visit both destinations.
It is a long days drive from Yellowstone to the Black Hills. So, to fly to Rapid City, rent a car, do a loop to Yellowstone and the Grand Tetons, and drive back to Rapid City to drop off the car and fly home, there are two long day drives accross Wyoming.
If the extra costs are not an issue, this vacation becomes easier without the extra trip accross Wyoming. I have no idea about bus tours. spiro is right on about lodging, it fills up fast. Do some price checking and come back with pointed questions, someone will be able to help.

We did do a car pickup at billings and dropoff at Jackson. There was no drop fees and the price changed very little. You will just need to check. Sometimes dropoff fees are big sometimes not at all.

What month? Things don't open up in Yellowstone all at the same time in spring.

Devil's Tower is just a stop, not a full day, couple hours at most.

Mt. Rushmore is likewise just a couple hours or so. It's cool to see it lit up at night but that may not be an option depending on flight times. Realistically you could have them see Devil's Tower in the morning, drive to Mt. Rushmore and then fly out that evening.

So depending on flight arrival/departure times, you could probably combine Devils Tower and Mt. Rushmore into one day, thus freeing up another day for Yellowstone.