From personal experience I'd say coffee is not always good for your mental state. If I drink a cup every day for a week I get into a constant state of anxiety and nervousness. I also get dizzy during workouts. I also can tell when my girlfriend had coffee because she will be much more combative in discussions.

As with a lot of other things observe yourself and don't blindly trust studies. even if the study finds positive results for 90% of people you may be in the 10%.