First, what I would consider the pros:
1. Very little in the bed of your pickup; just a ball and if you get the flip down; or B&W turnover ball, you can convert your pickup bed into a flat pickup bed in 2 minutes.
2. With a gooseneck ball you can tow many other types of trailers, giving yourself more flexibility.
3. With a gooseneck ball you only need to line up and get the ball under the trailer; with a little flexibility; and you don't have to worry about the exact height of the trailer, you just need to make sure it's high enough. With a fifth wheel plate you need to line up and have the height fairly close.
4. Most gooseneck balls have a higher tow rating; not that you pickup can handle that much, but knowing your hitch ball is far overrated for the trailer you are towing adds some insurance against failure.
Now the cons:
1. If you get the trailer with the gooseneck configuration I believe you would be limiting your resale market.
2. With a fifth wheel plate you can tow other 5th wheels. (Friends in need)
3. If you ever trade and chose a trailer that only comes in a 5th wheel configuration, you will have to buy a whole new set up.
So I guess it comes down to what you think you will do in the future. The B&W configuration would give you both options. You get the gooseneck ball installed and then purchase the 5th wheel adapter. It's a little more work to put the fifth wheel plate in, but not so cumbersome that it's a problem. I personally prefer the B&W because it gives me the best of both setups and if you compare the 5th wheel plate to others you will see the B&W is much more stout. That's not to say other plates are good or plenty strong; and most all plates remove easily leaving you only with two rails in the bed of the pickup.
Hope this helps; I'm sure others in this forum will be able to offer many different opinions, and that's what I like about this forum. There is a vast amount of knowledge which most are willing to share, and then you can make up you own mind.