The fifth wheel is the more stable of the two but it takes up more room in the bed of your truck. Also you may have fewer choices of trailers to pull with a fifth wheel setup. Example: Just between myself, my sons and my brother we have 7-8 different goose neck hitch trailers. We all have only two fifth wheel trailers.
In tight uneven spots the goose neck hitch lets everything flex more. On the flip side you have to balance the load more side to side on the front of your trailer or the trailer will be riding with a twist in it. The fifth wheel will stabilize the load side to side better.
Word of caution!!! IF you have fifth wheel hitch and have the trailer load not balanced side to side. You will be fine while you are in a straight line with the trailer. Turn where you are at a 90 degree angle and your fifth wheel hitch will then rock to balance the load. If the trailer is really out of balance I have seen the trailer hit the truck bed/cab when it gets around to a full 90 degree angle. Think about it. The hitch pivots front to back not sideways. So in a straight line your fine but when you turn far enough for the hitch to pivot you can get into trouble.
I like the goose neck hitches just because they are simpler. I also have hitches made for tractors or even my skid steer. So I can use the trailers with more things. It gives me more flexibility.