For reference, a 12-ounce can of Coke has 34 milligrams of caffeine, while an 8-ounce cup of coffee has between 70 and 140 milligrams depending on the variety and how it's brewed.
Some sodas have slightly more caffeine than plain Coca-Cola, but it's not usually a major difference. For example, a 12-ounce can of Dr. Pepper contains 41 milligrams.
If you prefer diet soda, it might have slightly more or less caffeine than its counterpart, depending on the brand. For example, a 12-ounce can of Diet Coke has 46 milligrams.