Kid #1 was exclusively formula fed due to a milk protein allergy. Kid #2 was exclusively on the breast. They are in elementary school now, surrounded by germs. No noticable difference between how often they get sick.

In the end, a formula fed baby was far less stressful for us. No worries about feeding or pumping schedules. No worries about if they are getting enough. With infants, a calm and non-stressed parent is best.