Huskerwater, I recently crossed almost all of the rivers mentioned on a recent road trip across Nebraska. I was driving from Denver, CO to Pierre, SD for a bird hunting trip. I drove out 76, then east on 80 to take 83 north into SD. With a short stop at Cabela's in Sidney, of course!

The Dismal looked swift, narrow and unmercifully winding where I saw it. Given it was early November, it still looked navigable for a canoe though. The Niobrara was much larger where I saw it near Valentine. Both looked like nice rivers.

If I recall correctly, the three Loup River branches were tiny creeks though were I was, along Hwy 83. I assume they might pick up volume as you move downstream.

The Sand Hills region was interesting to drive through. Very windy, with nice rolling terrain. Not many trees though, mostly scrub brush. I would bet you could do a trip down either river and probably never see anyone.