Of course, that's a completely unanswerable question, since "best" is extremely subjective. Here are a few I've seen, and how they rank:
Rodgers & Hammerstein's Cinderella
This one has nostalgic value for me, and I've always liked the extra songs that aren't in the Disney version. Though it's cheesy, I think I'l always have a soft spot for it.
Disney's Cinderella (1950)
I think I'll always think of this dress when I think of Cinderella's famous ballgown. While I prefer other versions over this one (the king's temper bothered me, even as a child) I have to admit, this version will probably always be the most influential Cinderella film out there.
The Prince and Me
A cute, if rather uninspired modern adaptation. I'm not sorry I saw it, but it's not one of my favorites.
Cinderella - The Whitney Houston Version
I've never been a huge fan of Brandy's voice, but Ms. Houston more than makes up for it.
What a Girl Wants
Amanda Bynes was never very high on my list, but I thought this adaptation was cute enough.
A Cinderella Story
Jennifer Coolidge is a fantastic wicked stepmother, but unfortunately I didn't find much else to like in this adaptation.
This one is hands down my favorite. I love everything about it, from the costumes, the acting, the script, and especially the gypsies. And the spectacular wickedness that is Angelica Huston.
Disney's Cinderella (2015)
I will definitely be seeing this (it comes out in just a few days) and will let you know how it ranks. I already give it points for its cast, though I'm really disappointed in Cinderella's ballgown. We'll see how it goes.
What are your thoughts? Do you agree with me? What's your favorite Cinderella film?