Django Model Mixins: inherit from models.Model or from object?

This is a question about Python Mixins that might be useful in general. I'm just using Django models as that is the use-case I'm most familiar with.

Should a mixin inherit from the class it is designed to mix-in with or from 'object'?

Examples by code, what is more correct or better, or better depending on what you want to achieve?

This

class TaggingMixin(models.Model):
    tag = models.ForeignKey(Tag)

    class Meta:
        abstract = True

class MyModel(models.Model, TaggingMixin):
    title = models.CharField(max_length=100)

Or this:

class TaggingMixin(object):
    tag = models.ForeignKey(Tag)

    class Meta:
        abstract = True

class MyModel(models.Model, TaggingMixin):
    title = models.CharField(max_length=100)

I think inheriting from object is the right way. But I'm seeing examples of the first case all over the net...

EDIT: I've moved my follow up question to a separate question: Django Abstract Models vs simple Python mixins vs Python ABCs