I had a grain gooseneck for several years, now I have a bumper machinery trailer.

There are advantages and disadvantages for both, but if you are going to load very heavy, I would lean strongly toward the gooseneck.

Others have mentioned better control, my biggest advantage was transferring weight to the rear tires with the gooseneck.  With my present bumper machinery trailer, if I load too much weight to the front, I can bottom out my ton truck with overload springs clear to the raised hitch jack.  I have to distribute weight more over the trailer tires, and lose some braking advantage to the truck, relying more on trailer brakes.

I had much better control with 350 bushels of corn on the gooseneck grain trailer than I do now with a small 656D with loader on the bumper trailer, a smaller load.  It all has to do with weight distribution.

All said, they both work.  I went with the bumper trailer because I didn't want to give up bed space for hauling other things, and it was much cheaper than a gooseneck.  There were other considerations in my choice, but they were minor.

 My opinion, if you are loading the trailer often, go with the gooseneck.  If it is only occasional, the cheaper bumper trailer will work if you are careful.  I don't load and pull often, just want to haul when necessary.