There is no definitive answer to this question as it depends on a number of factors, including the type of trailer, the load being carried, the terrain and conditions where the trailer will be used, and personal preference. That said, here are some general guidelines that may help you decide which tire type is best for your trailer:
D-type tires (also known as bias-ply tires) are typically less expensive than R-type tires (radial tires), but they don't provide as much traction or wear resistance. If you'll be using your trailer on paved roads in good weather conditions, D-type tires may be a good option. However, if you'll be carrying a heavy load or traveling off-road, you'll probably want to choose R-type tires.
R-type tires offer better traction and wear resistance than D-type tires, but they're more expensive. If you need extra traction or plan to use your trailer in rough conditions (off-road or in inclement weather), R-type tires are a good choice. However, if you won't be carrying a heavy load and don't anticipate any major challenges where you'll be driving, D-type tires may suffice.