In a deck over model, the wheels are underneath the dump bed. This means the wheel base is a bit more narrow and deck rides a bit higher. In a low profile model, the wheels extend beyond the width of the dump bed, allowing the deck to ride a bit lower. There are benefits and drawbacks to each style.
Some of the differences between these two dump trailer styles are subjective and will vary from one person to another, but there are some opinions that are pretty consistent. For instance, most people suggest that the higher dump bed of the deck over trailer provides a better angle for dumping loads. This allows a little more flexibility when loading the trailer, allowing loads to be stacked tall instead of spread out from front to back. If you will be quickly loading and dumping the trailer, and the getting the job done quickly is a priority, then a deck over model may be best for you. There are some drawbacks, however.
While the deck over model may provide a better dumping angle, the low profile model has some benefits of its own. First of all, if you are loading the trailer by hand, having a lower bed can make it much easier and faster than having to lift the load into the higher bed of the deck over model. Also, if you will be using your trailer to haul any kind of equipment (like a tractor or skid steer), loading and unloading your equipment will be much safer and easier in a low profile model with a better ramp angle. In fact, some manufacturers don't even put ramps on deck over models in order to discourage people from trying to load heavy equipment into it.
These are just a few of the differences to consider when making your next dump trailer purchase. Making the right choice really comes down to thinking about what type of work you will be doing and how you plan to use the trailer. Choose wisely and your new dump trailer will likely provide many years of reliable service.