The actual player on youtube streaming is wonderful. I can pause, rewind thirty seconds, watch that chunk again, then set my speed to 1.25x to catch up. You can't do that with twitch. You also can't show up 5 minutes late and watch from the start; anything between live and one-hour-delayed is a terrible experience.
The feeling I've gotten is from watching both is that I prefer YouTube for the actual watching (streaming just seems to work better, especially with being able to rewind live streams).
But I still prefer twitch for discoverablity and just easier navigation. YouTube Gaming[0] works ok (though most people don't even know it exists), but they try to blend live and past events too much for me.
