The Ozark Mts are north of I-40 (and the Arkansas River) extending into southern MO, and the Ouachita Mts are south of I-40 extending near I-30 and into the far eastern part of OK. I suppose there is a difference, but they both look the same to me. But both are beautiful country worth a visit. Kinda depends on what route you prefer to take, as there are many options. Or you can easily travel thru both.
We really enjoyed Petit Jean State Park, but that is a little more toward the central part of the state. Not far from Hot Springs which is also a pretty area, and worth seeing for the scenery and interesting town, but touristy.
The area up north around Eureka Springs is also beautiful, and the town is interesting in itself although again very touristy. And of course, Branson is not far away if you are interested in taking in any good live music shows.
SE OK, as I remember, is pretty much just an entry into the more mountainous areas of AR. Not to diminish the beauty of it, but don't remember much else being there.
