Here's all you need to know, courtesy of this super helpful website which gives calorie-to-alcohol ratios for many major brands. (The lower the ratio the better.)
We begin with Everclear is best, which with a 18.9 is the lowest ratio out there. (Anyone remember that frat party where they served Jungle Juice in trash cans? You don't? Hmmm...strange, that.)
Next best, and in the 19 range, are the hard liquors: tequila, rum, vodka, gin, whiskey, whisky. (It's the mixers you need to look out for, so soda water or diet Coke only, please.)
Wine shows up anywhere between 20 and 26, so clearly more research is needed in this department.
Most beers hover around the 27-30 mark.
And the worst drinks for your waistline are Bailey's, Kaluha, Godiva liqueur and other such rich drinks, which have scores in the 50s.
So! Bottoms up!