Most Efficient: Bud Select 55
A somewhat surprising result. This is definitely the beer to drink if you're ever in a situation where you feel you have to have a beer for social reasons, but would rather not be drinking anything. Because of the super-low alcohol content, it's sort of hard to recommend this one for getting your buzz on. You're going to be a frequent visitor to the bathroom. Bud Ice, the second most efficient is over twice as strong, but be warned: when warm, it tastes horrid.
Best Keg or Tailgaiting Beer: Natural Light (tied for #3 in Beer Efficiency)
As many college fraternities' keg beer of choice, Natty Light is indisputably the most efficient for the wealth inhibited. Beyond its caloric efficiency, it tastes OK for a domestic light and is dirt cheap because there is no advertising budget. Basically, an all-around winner. Well, except that it's somewhat unacceptable to drink and almost never found in bars.
Best Beer to Drink at a Bar: Miller Lite (tied for #6 Beer Efficiency)
Miller Light, known to some as Boggs, is readily available and shares none of the social stigmas of the top 5, ie. for single guys out there, you can drink this and won't scare off the ladies. Many bars carry it in bottle or draught form. Also the unofficial beer of the Jersey Shore. Whether or not that is a positive is up to you. Michelob Ultra (tied for #3) is an acceptable substitute, though harder to come by.
Most Efficient Malternative: Mike's Light Hard Lemonade
The majority of drinks in this class are loaded with sugar and should be avoided. Mike's Hard probably used some artificial sweetner to get the carbs down and make this a reasonable choice.
Most Efficient Malt Liquor: King Cobra
Its doubtful anyone who is drinking a malt, found primarily in bodegas and gas stations, is too concerned with efficiency. For the rare folk who is: King Cobra nudges out Sparks Light for top position.