The bottom line is that if a person is needing to replace the tires on their trailer, the first place to start is at the scales. Before we can make a determination of how much tire load capacity, and how much reserve we want, we have to know how much weight is pressing down on the tires.
Once the user has determined that, then looking at the tire companies website is an excellent place to start determining what is on offer that will meet the needs. The links in an earlier post to the Michelin site is a good example. One can click on the "75 mph link", and once at the the Michelin site, if you scroll to the bottom, there is a pdf document that Michelin provides that spells out the load and inflation tables as they apply to that tire in it's various sizes and applications. All of the major brand tire companies provide this information for their tires.
A convenient shortcut to much of this information is the tire rack website. They have compiled it all in a way that makes it easy to compare not only within a given tire manufacturer, but different brands ( that they carry obviously ) as well.
At some point in this entire process, the consumer has to determine what importance certain parameters play in the buying process. Speed rating, cost to purchase, how long the tire may last, availability of replacement of one or more tires should that become necessary, etc.
Obviously we are each price sensitive to different things. Many folks will buy the least expensive out the door product they can, and hope that it will meet their needs for the life of that product. Other folks may feel a better process for their own use is to spend a little more to buy something that is of higher quality or other attributes, and think their decision is correct.
I recently watched this scenario play out with my two oldest daughters. They both bought new cars in the last two months. Number one daughter chose a Toyota RAV4, and my other daughter chose a Mercedes SUV. Both of these girls ( and their husbands ) can easily afford pretty much any vehicle they choose....so it wasn't down so much to "cost of purchase", but more to what they each saw was important "to them" in the overall buying decision. To each their own....they are both happy with their choice.
My point is, it's good to make an informed choice when we buy something, and to be realistic in our expectations. It's good to look at the overall quality and reputation of any type of product we are considering, and think about how that might affect us in using it.
To go back to the very beginning of this, the OP asked, "what is the best tire for my trailer"......I think he has been given plenty to chew on, and lots of tools to help him decide. Only he can answer some of the "personal choice" decisions in the process.
Good luck and safe towing to all. Choose wisely and enjoy your trips.