A 12 ounce can of Mountain Dew contains around 55 mg of caffeine which is way less than coffee would contain.
If you drink a 16 ounce cup of coffee you would consume 320 mg of caffeine which is way more caffeine than the 12 ounce can of Mountain Dew contains.
Still coffee is the better healthier option for you to drink more of instead of the Mountain Dew or other sodas even when they're low on caffeine.
But since coffee contains more caffeine it tends to make you pee more often and faster because of the diuretic affect it has on your bladder.