The answer to this question, quite frankly, depends on how much of each you are drinking. It may seem that a standard 8 oz. cup of drip coffee has less caffeine compared to espresso, but it actually doesn’t.
Generally, an 8 oz cup of drip coffee contains around 94 mg of caffeine, whereas the caffeine content of a shot of espresso (about 1 ounce) is around 63 mg. So using this as a simple comparison, drip coffee wins the higher caffeine content battle.
However, espresso has more caffeine per volume than brewed coffee. For every ounce, espresso has about 40-55 mg of caffeine; drip coffee is only 9-19 mg per ounce.
The caffeine content of any coffee drink also depends on its serving size. If you make your espresso a double shot then you are getting either as much or more caffeine than you would with a regular cup of drop coffee.
However, it is very likely that you drink a lot more black coffee than espresso shots in one sitting … right? That means black coffee will serve you a lot more caffeine than Espresso, despite the latter having more amounts per serving than the former.