Montessori schools vary wildly. The name isn't trademarked so anyone can call themselves Montessori.
However, in my experience (admittedly limited to just 2 Montessori schools local to me) adhering closely to the original Montessori practices isn't necessarily a good thing.
When Montessori was first developed, the idea that play is the work of children was truly revolutionary compared to mainstream ideas about education.
But as a PP says, most of what was good about Montessori's approach has now been incorporated into the Early Years approach anyway.
Settings that aren't strict about sticking to Montessori rules are arguably likely to be better IMO as they're incorporating modern ideas on education with the best bits of a system designed over 100 years ago.
The strict Montessori school I visited was - ironically - overly prescriptive and although they claimed to be letting the children direct their own work, there was subtle manipulation into then doing it in a received and IMO stifling way. I'd expected to love it and I hated it. But that's just one place, visit your local ones and make your own mind up, I would.
Steiner? They're fucking bonkers! I notice that all the adults I know who attended Steiner now have mental health issues.