The short answer is: both.
Coffee and green tea contain different amounts of caffeine, brimming with antioxidants, they have some great health benefits. They are both safe and healthy– except for pregnant women– who might have to limit their caffeine intake to less than 200 milligrams per day as advised by the American College of Obstetricians and Gynecologists.
Although both green tea and coffee contain caffeine, coffee has a significantly greater amount per cup. A cup of coffee contains 100-150mg of caffeine, while a cup of green tea contains about 26mg.

1. Coffee vs. Tea and their health benefits

Both green tea and coffee do have various health benefits.
There is some evidence from Japan that green tea can reduce chances of death from all causes (23% lower in women and 12% lower in men). It can also prevent heart disease (31% lower in women and 22% lower in men). The results were particularly evident for stroke cases (42% lower in women and 35% lower in men).
Both green tea and coffee seem to help against developing type 2 Diabetes as well, although the case seems stronger with coffee. Studies show that those who drink coffee regularly have a 23-50% lower risk of getting this disease.
There is really conflicting evidence about green tea being protective against cancer. Coffee may reduce chances of liver cancer and colorectal cancer. However, liver cancer is the 3rd leading cause of worldwide cancer death, while colorectal cancer is the fourth. That’s pretty significant! Green tea may slow cognitive decline in the elderly at smaller doses, while coffee only shows the same effect after drinking large amounts. Moreover, the total caffeine intake in people seems to have a massive effect on preventing Parkinson’s in men; a reduction in risk ranging from 32-60%
Green tea seems to also lower LDL cholesterol and raise HDL cholesterol. Finally, green tea drinkers have up to a 31% lower risk of heart disease.

2. Metabolic rate and dental health

It is common knowledge that green tea is a fat burning drink, and may therefore assist in weight loss. Several studies show that caffeine can boost the metabolic rate in the human body by 3-11%. The effect is kind of small, but it still might be an important weapon in your fat loss arsenal. Green tea might help you with killing bacteria and inhibiting viruses like influenza, potentially lowering your risk for infection, and therefore helping improve your breath and oral health.
Coffee gives people that “coffee-breath” which some people find quite unpleasant. These were just the main points that have come up during my research of tea and coffee. However, the effect of these two beverages have been studied EXTENSIVELY. If you have the time and interest, you can find a ton of more information by going to Google Scholar and typing in words like “coffee”, “tea” and “green tea and coffee”.

Conclusion

Both green tea and coffee contain caffeine, as well as high amounts of antioxidants and some minerals. The health benefits from both beverages could be due to their antioxidant effects or because of something called “hormesis”. It’s important to know that the polyphenols in coffee and tea are foreign substances to the body, and might cause an increase in the body’s defense mechanisms. Of course, hormesis is definitely something that often occurs involuntarily, and is never encouraged to develop voluntarily. So don’t do it!
If you prefer tea, then you should continue drinking it. If you prefer coffee, then great. If you want to experience the best of both worlds then it might be best to drink a little bit of both. It’s always important to be careful of over consumption however, realizing that too much of anything is never a good idea!