OEM would be nice for the gooseneck feature. The total cost increase on the truck would be about $800, $500 for the prep and IIRC, $295 for the rest of the gooseneck stuff. If I were contemplating a 5th wheel and I were ordering a truck, I would NOT order the OEM prep. I would go for a B&W setup. I am initially very unhappy with the factory 5th wheel accessories. First, I have 5 holes in my bed compared to a B&W that has 1. Second, I had to buy a $575 rail kit t that only clamps down into the 4 holes in the bed and then I have to supply the actual 5th wheel hitch. Third, this rail kit is rather heavy and cumbersome for 1 person to install in the truck. It took three men to install it the first time. I haven't put it in again. I am hoping that some adjustment and settling from the weight of my 5th wheel will make it easier than the first time. Fourth, when I was disconnecting my trailer the last time, the front two pins came out of the bed. Not sure why this happened as the Ram guys installed it (taking out MY user error) but it certainly does not inspire confidence in the design. Fifth, to total it all, $500 prep, $575 rail kit, ~$600 for a decent, heavy weight hitch, you are at the same price as a B&W with Companion installed without all the extra pieces and hassle that goes along with OEM.
The gooseneck looks nice and easy. Again, this is just my first experience with the 5th wheel attachment. Hopefully by the third time it goes piece of cake.