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I can only write about FormWizard as I have used it before. According to ‘Handling Files’ section of Django documentation which can be found in
https://docs.djangoproject.com/en/dev/ref/contrib/formtools/form-wizard/
a FileField can be used in any step of your FormWizard implementation. What I found really helpful by using FormWizard from Django, is that it provides you all the standard functionality of Forms. That means that you can easily create and manipulate forms, validate fields in each step, etc. I am not aware of how CSS3 slider accomplishes validation, but I guess that validation should take place on client side.
Additionally, Django’s FormWizard uses either a Cookie storage backend, or a Session storage backend in order to store information, which makes the navigation between steps and modifying previous stored data pretty trivial.
I hope I helped you in your decision! A lot more information can be found of course in the Django documentation of FormWizard in the link I provided above.