Is it permissible for a traveler to break their fast for three days in Ramadan if fasting affects their concentration at work, and is it better to fast or to break the fast?

It is better for you to break your fast in this situation because fasting is difficult for you and affects your work. Allah loves that His concessions be utilized, especially if this results in benefit for Islam and Muslims. Indeed, those who broke their fast today have earned the reward.