Sugar? No added sugar in a margarita.
Margaritas are made with tequila, orange liqueur (this has sugar) and lime juice. With ice, a lime wedge and salt.
Usually the proportion is 3/2/1.
And I totally agree that you should always use good tequila, though really
good tequila is wasted on a margarita IMO (it's a sipping liquor).
Tequila, by definition, comes from the agave plant. It has to be at least 51% agave but is allowed to be 49% other stuff, usually corn or sugar-based liquor.
Gold tequila labeled "oro" can have all kinds of artificial colors and flavors and crap added, in addition to the non-agave liquors.
My usual go-to is "reposado" which is also almost always 100% agave.