I used Twitch before youtube gaming came out so I'm on the twitch side (well used to before I stopped on a break.....a long break
))
But if you have the Youtube following then I would stick with Youtube for streaming, Or if you're not partnered on Twitch, use a multistream service which will beam your broadcast to both Twitch and Youtube and then advertise yourself on Social Media.
With the multistream service I'd have a little research about it first, since I'm not sure if it states in the terms on YT or Twitch (If you're partnered) that your stream is meant to be exclusive to that platform.