Classes definitely give you a lot of rope to hang yourself with (metaclasses, inheritance, MULTIPLE inheritance), but they have their place. I'll usually start with a function, but when it gets too big, you need to split it up. Sometimes helper functions is enough, but sometimes you have a lot of state that you need to keep track of. If the options are passing around a kwargs dictionary, and storing all that state on the class, I know which I'd pick.

You can memoize methods to the instance to get lazy evaluation, properties can be explicitly defined up-front, and the fact that everything is namespaced is nice. You can also make judicious use of @staticmethod to write functional code whenever possible.