When we begin our own primary (ages 3 to 6+) classrooms, we need to make a decision about our sandpaper letters and movable alphabet--which font do we choose? But, many of us inherit a classroom and must use the font we have. Or, we must follow the culture of our school so there is consistency from room to room. In any event, this is a topic Montessori guides consider deeply.
Unfortunately, I have not been able to find any specific, convincing studies that directly answer the question of which font is preferred. This is why Maitri Learning offers our movable alphabets in all three of the fonts commonly used for the sandpaper letters.
The question of font, however, has been indirectly answered.