I've done both. For sheer numbers, Nebraska is hard to beat. Tons of birds and very high success rates. That said, but the state is mostly hybrid birds save for the panhandle region. Those hybrid birds get absolutely huge, but if you're going for a Grand Slam, it may not be your cup of tea. I shot you a PM with some info on the very productive public land options you have, especially if you decide to hit the eastern half of the sate.
For a shot at a pure Merriam on the abundant public land in the Black Hills, SD is excellent. You can get into a small population of Rios in the northeast corner, but a lot of that land is private with no access assurance. Conversely, I saw plenty of Merriam's gobblers on the western public lands. Technically, you can legally hunt any non-posted public land in the Black Hill unit, but I would definitely get verbal permission before accessing someone's place.
Last edited by Six-Gun; 03-01-2020 at 07:37 AM.