In the past the answer would have been clearly Twitch, today YouTube has also done well and is a great option. I've never streamed before, I think my quality is okay. Would set 720p60 and choose Fortnite as the game. There are countless streams on Twitch, I personally don't find that many on YouTube. Which is better to start?
Basically, Twitch is better for most because of the community. However, we assume that YouTube will also become a huge factor over time, as Google invests a lot in the subject of live streaming. Both platforms have their advantages and disadvantages. We would recommend Twitch first.
I think YouTube is better. But not because streaming on YouTube should be better. More because you are more popular there with videos than on twitch. And after you've built up a small community, you can direct YouTube to twitch, where you also stream.
Twitch has more options to interact with viewers and generally more options to personalize the stream or profile.