Compare the size of the blades to sizes of tires -
the 28 mm to a kid's tricycle wheel/tire
the 45 mm to a car wheel/tire
the 60 mm to a semi-truck wheel/tire
The very bottom line is that they all cut fabric one thread at a time.
The bigger ones (60 mm) are better for thicker fabrics and more layers (think trying to get through snow or mud)
The smaller ones (28 mm) are better for tighter curves than the larger ones. (think of a shovel instead of a bulldozer)
For most people, if they can only have one, the 45 mm is the one to get.