When it comes to mixed drinks, there are three ways people generally like them. Weaker so the calories are lighter, at the recipe level mix so they're neither too strong or too weak, or they like them strong. When it comes to mixed drinks there are several different factors that come into play when trying to tell apart the "manly drinks" from the "girly drinks."
Proof can differ
One important thing to think about is the proof of the liquor being used. Not all rums are equal, not all vodkas are equal, and not all whiskeys are equal. Some are simply more alcoholic than others because they have a higher proof. Likewise a lot of the time vodka will generally be a little bit weaker than whiskey, and rum can vary a ridiculous amount from one brand to another. Just look at Bacardi 151, which is 151 proof compared to a normal 75-80. That makes any Bacardi 151 cocktail much stronger than its counterparts.
The mixing does matter
Whether the bartender follows the conventional recipes with perfectly measured shots or pours it on - this one thing can have an incredible difference when looking at how strong your drink is. What's one shot of whiskey versus the equivalent of two and a half or three? It's the difference for many people between the bar they don't go to and the favorite one that they do.
At the end of the day the recipe for a drink matters. A Long Island Iced Tea, for example, is a recipe that has four shots of various hard liquors, not to mention many recent versions also having a dab of triple-sec to boot and some cola because carbonation just gives it that much more of a kick. Compare that to a fuzzy navel which is the generally much lower proof peach schnapps and orange juice. In fact made to recipe, it might take 4-5 fuzzy navels to match a Long Island Iced Tea. Some cocktails are simply going to be stronger than others.
So what cocktails are tops?
This is a difficult question to answer because with so many pseudo-cocktails out there, over-proof rum, and insane combinations involving energy drinks, it's hard to get a handle on what exactly is "strongest." However some of the classic favorites that are hard to beat include the aforementioned Long Island Iced Tea, Zombie, or Aunt Roberta cocktails. There are many more modern ones that can certainly give the old classics a run for their money, as well!
When you're looking for the ideal strong alcoholic mixed drink, it always depends on what your tastes are. Some people love the idea of a Long Island Iced Tea while others just don't like that mixture of liquor. Next, some people love the extra caffeine and carbonation effects that come from cocktails mixed with energy drinks. Other people find that combination to be an absolute gut bomb. The good news is that there are so many really potent yet good tasting alcoholic cocktails out there that you should have no trouble tracking down one that works for you. So enjoy!