We have all probably seen this question on an RV forum or two. The problem is that many people have their personal choice but I doubt that any person has ever done any extensive controlled testing. If you think about it, why would anyone have a favorite brand but would be running a different brand unless forced?
As a tire design engineer I always depend on facts and data, and try and stay away from just an opinion. However since there is no way I can do a comparison of dozens of different brands in dozens of different sizes I do have to fall back on "opinion". BUT if we think about tire performance and durability in general I think we can come up with some information that can guide us to a shorter list of potential choices.
All tires have a "Material List" molded on the sidewall. Based on this information plus a few generalities I think we can develop a plan.
Looking at your current tires you will see what materials are in your current tires. I suggest you write the information down so you can keep the information organized.
Lets talk about tire construction. Modern ST type radials will usually have one or possibly two ply or layers (we can use the terms interchangeably) in the sidewall. The material used is usually Polyester. They will also have two ply of steel belts in the tread. Now this is the important detail. Some tires may also have one or two ply of Nylon or some other material in the tread in addition to the 2 ply of steel. This is the important part.
Radial tires have a high stress location at the edges of the belt. I have a number of posts on my RVTireSafety blog that focus on this force (Interply Shear) and location. Here is the most important one
One way that tire companies can address the Interply Shear and end up with a tire that might perform better on the special tests like High Speed that tires need to tolerate if they are going to have a higher "Speed Symbol" marking is to add a ply of Nylon on top of the steel belts.
Now the problem you as a consumer face, is that not all tire companies report the materials in their advertising. But the good news is that the information molded on the tire sidewall must, by law, be accurate. So if the tire says it has Nylon ply it must have the Nylon. Now a performance improvement is not guaranteed but in general, it is likely that tires with Nylon ply above the steel belt edges can have lower Interply Shear forces which should perform better and possibly longer. So lacking any other data, I would use the Nylon as a plus for a tire if I were considering two different brand tires.
You may need to talk with a tire dealer and possibly need to confirm yourself what the material list on a tire actually says.
You can confirm which ST type tire you are considering has the Nylon cap ply and which does not. If they are different then it is possible that the tire with the Nylon might be a better choice. Please remember that this is not an absolute, as without actual performance data we can not be certain of the future performance. But this is something we can consider and this data is better than just a wild guess.