^ I'm dead serious, never heard of it until I saw this thread, don't do that face man. ?
The people I watch still stream on Twitch and all the people I know only ever heard of Twitch for live streaming. I guess Mixer it's not that popular (yet) where I'm from, so I guess I should also advise you, @Toothless, to take this in consideration too when choosing which streaming platform you'd like to use. It really depends whether you plan to stream for a specific region (like your country, maybe you're not a native english speaker and you'd like to stream in your own language, therefore a smaller audience which may or may not heard about Mixer) or the whole world.
Just make sure the audience you're targeting is well aware of the platform and both you and your audience are comfortable using the platform. If you're still in doubt, try both of them, and you should be able to tell in a couple of days which one feels better/right for you and for those who watch/will watch you.