Creating a Python class for "just one instance"?

I'm asking this question with regards to Python, though it's probably applicable to most OOP languages.

When I only expect to use the data model only once in any program, I could either make a class with class/static methods and attributes or just make a regular class and instantiate it once and only use that one copy. In this case, which method is better and why?

With python, I could also write a module and use it like I would a class. In this case, which way is better and why?

Example: I want to have a central data structure to access/save data to files.

Module way:

data.py

attributes = something
...
def save():
...

main.py

import data
data.x = something
...
data.save()

Class way:

class Data:
    attributes = something
    @classmethod
    def save(cls):

Data.x = something
Data.save()

instance way

class Data:
    def save(self):

data = Data()
data.x = something
data.save()