If you're looking for a Facebook and Google Hangouts IM all-in-one on your Mac, Flamingo may just be your best option.
Flamingo only very recently launched and is easily a dream to use compared to other IM clients. It features an all-in-one design to keep everything nicely compact. But you can detach conversations from the main window to make it even more contact, if you're mainly just messaging one person.
Unlike other IM apps, it has an awesome inline media feature. So if you share something like an Instagram pic or a YouTube link, it can show a preview right there alongside your messages.
You can share files via direct connection or have them automatically upload to CloudApp or Dropbox for easy file sharing.
The app beautiful too, the UI itself and animations are stunning and just make it a joy to use.
Currently the app supports Google Hangouts, Facebook and other XMPP services. I'm a user of both Hangouts and Facebook and it can be a pain having to access two different sites to reply and send messages. An app like this makes it much easier.