OP, I guess you are speaking of the settings of these two systems and not quite the systems themselves. FYI, Pathfinder was derived from D&D 3.5 edition, and is sometimes referred to as D&D 3.75 edition.
As for the settings, comparing the Pathfinder setting of Golarion to the D&D 5th edition default setting of the Forgotten Realms, it is hands down Forgotten Realms for me. In fact FR is my #1 fantasy setting of all time by a wide margin, across not only RPGs but also movies and TV shows and novels. But having now played in the Golarion setting, it is beginning to grow on me.
