The best of both worlds is a BW Companion hitch. I have a gooseneck hitch in my superduty and then the companion hitch drops in to the gooseneck hitch. You can easily remove the hitch and have your flat bed floor.
I went with this option because I tried the gooseneck conversion and noticed some odd trailer movement especially going down hill. I agree with jbirrell I was also told it would void any and all warranty if I went with a pure gooseneck conversion.
Bob, Mallory and Alexis in Linwood,KS
2011 Ford F250 Lariat Crew Cab Shortbed, 6.7 Powerstroke, 3:55, Custom Spring Pack
2011 V-Cross 275VRLF Fifth Wheel
B&W Companion Hitch