This would be for a single axel boat roughly 3000 pounds dry, 14 or 15 inch rim, I forget. Some say the LT would run great and that the ST tends to be not so good. Any thoughts?

I run LT tires on a utility trailer and have had no issues. If you look at the tires used by roofers on their trash hauling trailers they are typically mismatched LT tires. I'm beginning to believe that trailer rated tires are just a way for rubber companies to work off their misbatched or overages rubber stock. But that is just my humble opinion.

Do NOT put car tires on that trailer.
I inadvertently bought car tires for my single axle boat trailer that towed in around 3500 lbs and they were the most miserable riding tires ever. When I finally switched over to Marathon ST tires there was a world of difference in how the boat towed and rode on the trailer.
I've used Marathons ever since and don't regret it for a second.
LT tires? not really sure why not, other than my experience with those horrid mispurchase while on the road after throwing treads on 7 year old carlisle bias plys.

I'd go for the ST tires & make sure you get the correct load rated tires. Single axle trailers usually have a higher load per tire so its important to get the right ones.

If 14" rims, finding LT tires might be difficult.

Most single axle trailers will have 15" tires to carry that much load.

My Jetboats run car tires, load about one ton, one axle.

Her Magnum 2450 runs 2 axles, trailer tires.

Dad's car-transport flatbed, I'm not sure what they are, are either car or truck tires tho I think, 2 axles, I'll look later.

Frankly, I agree.

They don't seem to last near as long as they used to.