I worked child care for over 10 years in many different roles, from nursery teacher up to being the owner of a child care center with nearly 60 kids enrolled. One of the places I worked as an assistant directer was a Montessori style child care center and I absolutly hated every day I had to go to work. The kids in 3 yr. class would run around wild for hours and not do anything. The 4yr classroom was even worse. They would climb on the firniture, bookshelves, etc...and jump. They tore up books on a daily basis and the director acted as if this was normal behavior for kids. They naever sat down and wrote their names, didn't work on colors, didn't do anything together as a class, they just played all day.
Nearly every kindergartener would come in from school with a note that said it took hours for the child to calm down and be able to sit at his/her desk and pay attention. The ones that didn't bring a note were the ones that didn't come to child care before school, their parents dropped them off on their way to work.
I like structure, I like having kids sit down and have work to do like write their names, copy the letters of the alphabet, color, paint, do a craft with the class, not run around during circle time and disrupt the class or throwing their journals in the doll beds so they wouldn't have to draw any pictures.
I know the importance of play, I know what kids are learning when they play, I know that kids also need some structure to their day. Not hours and hours, but some sitting at the table and following directions.
If you think your child just needs the interaction with other kids and no structure then choose Montessori, it is beneficial to some. At 3yr.s old it isn't really going to make a lot of difference.
But if you want your child to enter Kindergarten at 5yrs. and know how to write their name and maybe be sounding out written words then choose the school's pre-K program.