I went to all three stores and tasted their coffee.
The coffee at mcdonalds and starbucks tasted the same to me, but the one at dunkin donut tasted different.
I liked the one at dunkin donut best.
At first I thought it was because mcdonalds and starbucks used arabica beans but I checked dunkin donuts and they also used those beans.
What actually is the difference of their ingredients that makes them taste so different, even though they're both coffee?