This is gonna sound weird, but I find Twitch works more for two things:
2.) People who already have a pre-existing audience.
Most people who go to Twitch go to Twitch because there's a specific user they want to watch, a user who's already famous as fuck (ex. SummerGamesDoneQuick, TwitchPlays, etc.). Whereas Picarto is a lot easier to build a userbase on. Plus Picarto is actually built for artists whereas Twitch is built for broadcasters (and when I say that I mean like, people who offer up an entertainment service vs. an artistic one, so like gaming, show episodes, podcasts, etc).
So if you're an artist with a small fanbase, Picarto is your best bet. If you're a famous streamer who does all kinds of things besides art streams, Twitch. And whatever you're comfortable with using, really.