SAFD: Love this topic! My favorite spot is probably early AM loops between Poly and GF, which was made even better in recent years with the new GF to MK path since it added materially to the possible distance. If it’s late enough and you don’t mind stopping briefly at security there and back you can even continue on to CR and cover more ground, although I’m usually too early for that. There’s just something so peaceful about the Seven Seas Lagoon vibe early in the morning before most people are up.
Of course the former awesome stretch between Poly and GF is detoured at the moment given the Poly DVC tower construction. I will forever miss that peaceful stretch and hold fond memories of the many miles logged with the way it used to be.
I also like the Crescent Lake resorts - same early morning vibe logging miles. Always seem to be a lot of runners out so that’s nice.
WL used to be an awesome place to run until Disney removed the path to FW when they started (and then stopped) Reflections, so it’s totally cutoff and very difficult to log miles other than just going around and around the resort. I leave politely worded (

) feedback about that every time I stay there as it annoys me to no end.
I stayed at FW this past November and that was a great place to log Dopey training miles since you can cover a lot of ground and can manage repetition with all the choices of sidewalks and loops.
Honorable mention to CSR - while rather short, the resort loop around the lake makes for a pleasant run.