This debate has raged for years. Short bed you save roughly two feet. You loose 2 feet of useful bed space for storage. Long bed usually will ride a bit better. Long bed will usually have better resale value. Short bed usually has a bit better turning radius. It all really depends on what you get used to. I like my long beds better for the better looks.
BTW, if your going fifth wheel skip the 2500s and go straight to the 3500SRW. Right now the cost difference is only a couple hundred dollars new. Value if you go to a a bigger fiver in a few years and dont have to rebuy the truck........ PRICELESS!