Margarita....

"White" Tequila, and the medium priced brands labeled 100% agave work as well as any, although I'm emotionally attached to Sauza. The key? "White" usually has a harsher bite, better in a cocktail w/other ingredients.

"Key" limes, not "Persian" (and a good cast metal squeezer is an indispensable bar tool)

There's a long dispute over which "orange" liqueur, Cointreau or cheaper Triple Sec (Grand Marnier's both expensive a "chi-chi"). Old timers are quite happy with the Mexican domestic imitation, "Controy".

My formula ("Dry"): 2 parts tequila, 1 part lime juice, 1/2 part orange liqueur, shaken and served "Up".
No salt, but then Margarita's are traditionally consumed with a savory appetizer or salty bar snack.

Rose's lime juice, developed by the Brits as a scurvy preventive, has no place in a Margarita, not does any other bottled (and preserved) lime juice. "Sweet & Sour" mix or concentrates? About as far from lime or lemon juice as you can get, plus enough sugar to damage a diabetic. "Sweet" has no place in a cocktail already sweetened with orange liqueur, and then there are the preservatives and stabilizers in goat-choking quantities.

For an interesting variation, try using lemon juice instead of lime, and Italian "Lemoncello"
for a touch of sweet (and lemon peel zest).