In my experience of streaming, Twitch gets a broader following. It may be a tad more slow or buggy but I haven't noticed. Personally I am a little uncomfortable with more people or the idea that I need to do more to become a "streamer" in that kind of community. But I've met some good people through twitch as well. With Picarto, it is more art related and a tad more private feeling. There's still a big community though but less of a pressure I think.
I've been using Restream to stream on both Picarto and Twitch and I know you can add other things like youtube (Personally I don't like youtube's chat, but if you're just thinking video then I'm sure it's fine).
The only issue with streaming on multiple platforms is your followers are a little divided. I've seen that sort of resolved via viewing the chat in the window.
Really depends on what you prefer. I've been doing art streams on Picarto and find that it's a pretty good platform, for the most part. I get a reasonable amount of inflow of new folks just from the platform. If you're doing art and are just worried about streaming, it's a good option.
Twitch is definitely more gaming-oriented, though I personally plan to start simultaneously streaming there in the new year since I think there's more potential for actually making some money from streaming. The design of the platform is definitely better suited to that, though I haven't streamed art there so I can't advise much on that front. Do have some friends who do art streams on Twitch though.
A newer one I've heard about on rare occasion is Piczel.tv, which I think is another art-oriented platform? I know next to nothing about it myself, though.
I use mostly Picarto recently because it is built for artists. I can tell lot are still in YouTube but Picarto does have lot more setups like as picture panels and commission mode and you can even live stream with others as in multi stream. Twitch seems to be more for gamers but there is a creative side for it. However what you can do if don't want to choose is just use all 3 I use restream.io which you can live stream in all of them at once and have a multi chat to see what everyone saying ^-^