Liquor is made by distilling a grain, which means converting its carbohydrates to alcohol via fermentation. For this reason, distilled liquors, such as vodka, rum, and whiskey are at or near 100% efficiency (defined as percentage of calories from alcohol). Liqueur has added sugar, so watch out. Those calories can sneak up, just as those from mixers.
Lets take a look at some common liquors and how efficient they are. Keep in mind that 80 proof vodka is 80 proof vodka from a nutritional perspective. While Grey Goose might taste better and give you less of a hangover than something out of a plastic container, they can be considered the same for calories.
The below liquors are available in the Virtual Mixologist. We use carbs in the information, because unlike beer, there is no protein to consider. 1.5 oz. is considered a shot. ABV is proof divided by 2.