Well, I'm not sure, is Spaghetti better than Lasagna?
Ok seriously. No good way to answer your question as an LT tire is intended for passenger-carrying vehicles while ST type tires are specifically designed for trailers not carrying any passengers.
The Load formula for these two different type tires is different, just as the formula for P-type or passenger car type tires are different. ST type tires are rated for about 15% greater load capacity, depending on the specific size, but with a max speed of 65 mph. So if you never exceed 65 mph, ST type is "better" as they are rated for higher load.
DOT testing for LT type tires is more substantial (more difficult) and has more requirements than the requirements for ST type tires. So if you believe that being able to pass more difficult tests indicates a "better" tire and you want better durability then LT tires are better.
Now if you want to compare two different size or different Load Range tires but the same load capacity then IMO most LT tires are probably better than most ST type tires based on their ability to pass the more difficult DOT tests which are based on load.
What if you consider lower-cost your "measure" when comparing tires you might find that many ST type tires have a lower price than many LT type tires.