tldr went to Montessori, thumbs up.
I went to a Montesorri school from 1st through 4th grade.
I enjoyed the atmosphere. In recent years I've read about Montessori and found that my Montessori experience was different, but much the same wrt a gentle focus on practical individual learning.
Non Montessori school was a process of checking boxes and actual thinking inbetween, while Montessori was a cycle of thinking through problems for yourself, sometimes as a group.
One thing I didn't appreciate until later school years is that Montessori blends different ages and skill levels together. I neither felt the need to keep up nor to excel, just to figure stuff out. For example, I remember a a classmate writing an essay using movable letters on a mat, but he didn't space them out so it was hard to read. I asked why he was doing it like that and the teacher responded that he had chosen to do it that way, I felt it was wrong, but instead of letting me get on a high horse, the teacher drew my attention to what I was already on my way to do. He continued to write without spaces, and I continued to think someone should correct him. Lo and behold, he learned to use spaces, all without someone, teacher nor child, scolding him, with words or with red marks. That's hard to do in typical bureaucratized classroom.
If I were pressed to find fault in Montessori itself, I'd say, it cannot succeed at all without good teachers/emotion/energy conductors, while a common classroom can get ok enough outcomes with an authority figure and good textbooks.