Considering that ethanol is the highest contributor to calorie count of a beer, and that the amount of remaining ingredients only vary to a degree, while variance in ethanol is very high, the odd modern beers with extreme extreme alcohol content will be the most calorical.
It appears currently Brewmeister Snake Venom is the top alcohol content beer, at 67,5%, with 2025kcal in 12 fl.oz serving. The alcohol content runners-up don't top that by means of excessive sugar levels, therefore we can safely assume this is the most calorical beer.
Of course the competition in topping that is sharp, and we're soon to expect other beers with even more alcohol - and more calories as result.
There is no plain visual criterion to what beer has most calories, but you can safely correlate stated alcohol content with that.
...also note: Alcohol is empty calories - calories that are not absorbable - storable by human organism. A good mild caramel beer of 1.5% alc. content might be more fattening than the top alcohol content beers, simply because it contains more sugar.