For goodness sake, ask your bartender what the hell the well is for your particular cocktail. For example, if you’re ordering a gin and tonic (a highball, not a cocktail, but that is another post), find out what he or she will use.
Yes, even for a highball, where the amount of mixer, never mind the crushed lime wedges, helps to mask liquor quality. But even an ocean of tonic water won’t hide truly atrocious liquor.
Unfortunately, many bars have well liquors that are, well, atrocious. Often these “liquors” are in effect flavored neutral grain alcohol, often mixed by one or other of the big liquor distributors (a different system state-by-state, by the way, but more sometime later on this as it affects cocktails): juniper flavors added to the industrially produced grain alcohol for gin, while the vodka is that alcohol without the flavorings. I’ve seen “blended whiskey” that has caramel coloring added to it, to make it look like Seagram’s V.O. or Canadian Club, and the amount of actual whiskey in the bottle is anybody’s guess.
A better bar will have decent liquor in the well. For example, at Castle Street Café, we use Beefeater London Dry Gin in our well, and Dewers White Label for our Scotch, and Four Roses for Bourbon, Smirnoff No. 21 for vodka, Don Q Blanco, Gosling’s, and Captain Morgan Spiced Rum for the various rum categories. I haven’t settled on a tequila (well, two: blanco and reposado), but I’m guessing Espolan, a solid quality at a good price in this generally over-priced category of liquor.
If you are going to drink, drink well, by which I mean quality liquor.