The best Tequila you can get is called Herradura Seleccion Suprema. This is aged for 5 years and is a very smooth Tequila. It is an ultra anejo tequila, these are the ones aged and that is what makes a great tequila.
Patron, without a doubt. It's 100% agave which makes it a smooth tequila that you can actually drink on the rocks. And if it's good on the rocks, it great in mixed drinks. It doesn't have that bitterness/aftertaste that other tequilas do. Depending on size and type it can run from $50 to over $100.