Should I use a class or dictionary?

I have a class that contains only fields and no methods, like this:

class Request(object):

    def __init__(self, environ):
        self.environ = environ
        self.request_method = environ.get('REQUEST_METHOD', None)
        self.url_scheme = environ.get('wsgi.url_scheme', None)
        self.request_uri = wsgiref.util.request_uri(environ)
        self.path = environ.get('PATH_INFO', None)
        # ...

This could easily be translated to a dict. The class is more flexible for future additions and could be fast with __slots__. So would there be a benefit of using a dict instead? Would a dict be faster than a class? And faster than a class with slots?