Finding a good margarita at WDW is a constant challenge.
I like the Dragones Top Shelf at Cava del Tequila, but it’s pre-mixed (like most there) so sort of annoying.
I usually try to make nice with the pool bartenders to get a better one. Sometimes need to order a double to make it tolerable as the default setting at so many places is too much mix.
The Patron Top Shelf at Siestas Cantina (CSR pool bar) is good. Basically anywhere at CSR makes good ones - Three Bridges, Dahlia Lounge, etc.
Dawa or Thirsty River Bar at DAK are good, just stay away from the pre-mixed ones.
Favorite margarita on property is the Ancho Spicy Margarita at California Grill.