IMO, hangouts is infuriatingly bad. It's way too keystroke-intensive to sign in and sign out of accounts in the iOS app; the Chrome app (plugin?) thing is terrible and the functionality seems to change every other week.

I can't count on them not breaking notifications (such as those for when I receive a message while signed out) in new and exciting ways at random times, and... well, it's just terrible in all kinds of ways.