R4 advantages over R1/Ag: longer service life on hard surfaces, higher load (weight) capacity, more cut / puncture resistance, less damaging to turf / dirt trails.
R1 advantages over R4: better traction, better ride quality.
R14: marketed as a R1 - R4 hybrid. Folks seem to like them on utility type tractors but I have no direct experience with them.
What tire is best for your applications is almost always a compromise of some sort on a utility tractor because it’s used for a wide variety of jobs.
A 35 degree/70% slope is steep even for a 4WD tractor, and never sideways. If I couldn’t traverse grades that steep, I couldn’t access well over half our property. 4WD with R4’s handles it FAR better than 2WD with R1’s and causes less damage to our dirt trails. We don’t have rocks. Ability to go up and down safely depends on a variety of factors. There are some pretty good threads on here discussing the issue.