Should I set initial state in the reducer default arguments or in the default store?

Question

I am using redux, and need default values for my app state. For example the default User is false as by default nobody is signed in.

Should I set this in the reducer itself as follows:

const User = (state = {current: false}, action) => {

Or should I set them in the default store as follows:

import defaultstore from './defaultstore';

const store = createStore(reducers, defaultstore, middleware);

Which is preferred? What are the pros and cons?

I find Redux documentation confusing as they use default values directly in the reducer here, but at the same time they pass them in as the second argument in createStore.

How do I know which is best, i.e. requires less maintenance ( less refactoring, easy troubleshooting ), works efficiently ( Big O ).