I don't think you would have any difficulty on either of these routes. Both are US highways. They will not be straight and level, but I've never found any problem in towing a 34' fifth-wheel on either.
I have found the state highways in Arkansas to be very "wind-ey" and a good bit of up and down. I just decide to enjoy the journey and know that I cannot make the kind of time that I would on a freeway or even on a US highway.
To your question: I've been over much of US 270 and US 71. Mostly 2 lane and helps not to get behind a log truck, but I don't see any reason for concern--no switch backs; no really steep grades. Now if you go up to Queen Wilhelmina State Park on Rich Mountain near Mena, you can find a bit of both.