I'm sorry to revive a nearly 4 year old thread, but I have to.
I like margaritas made from scratch, anything made with a mixer or in a bucket is crap. My personal favorite tequila is Patron Silver, it is so smooth and flavorful without giving you the gaggy "get super drunk" alcohol kick.
But rather than a margarita, I like to drink a Mexican Martini which anyone from Austin can tell you is a food group in its own. I've tried different recipes that use sweet 'n sour mix and different things but this one is my favorite. Salt the rim of a martini glass and drop in an olive or two, I prefer jalapeno stuffed olives. Then mix equal portions of 100% agave tequila, Contreau*, fresh squeezed lime juice, orange juice (fresh squeezed is best), and sprite or 7 up. Shake well, pour, and serve.
*I actually make my own mock-Contreau. Dissolve 3 cups sugar into 2 cups of water over medium heat (a simple syrup) and let it cool. In a large jar with a lid, stir the zest, juice, and pulp of two oranges into a quart of 80 proof vodka (Tito's is my favorite [also from Austin], but for stuff like this I usually get the cheapest stuff), and stir in the simple syrup very very well. Let this sit for 2 weeks, shaking every day. Strain out the solid parts and re-bottle it and enjoy! This is great because it is pretty darn close to the real thing and you probably won't have much more than 10 bucks into a huge jug of it, but a smaller bottle of real Contreau is over $20.