I don’t have any preference, but I think a horse trailer it’s more convenient. With my experience, a horse climb more easily in norse trailer, because it’s longer and the horses dare to go there
And I think it really depends on how often you use it as well. I had to take a trailer test. But decided trailer was better for me as I needed a car anyway. But trailer costs me nothing sitting there, with a box you have the cost of 2 vehicles to go wrong.
I hope this helps.
I prefer slant loads to box trailers because they tend to be heavier, which means more security in the case of an accident, and less risk of being blown by wind slipping etc. Whenever we hire people to trailer out horses, we like to have bigger trailers with more horses in them for the safety