>>59512754tl;dr for streamers, Youtube is better for straight streaming, much less so if you are dreaming to make it big. For viewers, it's much better if you are a passive viewer, infinitely worse as an active viewer.
Youtube streaming is fine. It's building an audience there that is harder. There's no good way to browser currently live Youtube streams. The search function just stops giving you results after a while, so searching for currently live streams for a game won't actually show you all the streams currently live for it.
As a streamer, streaming to Youtube is no harder than streaming to Twitch, and lets you give it a much higher bitrate to leverage their specialized hardware for transcoding the stream. They do bitstarve streams fairly heavily, with 1080p60 being set to ~4500kbps average, and 1080p30 set to like 2500kbps average. But for 1080p60 that still tends to look as good or better than a 6000kbps 1080p60 Twitch stream, because of course the specialized hardware will do a better job 9 times out of 10.
It won't outperform partners utilizing the 8000kbps bitrate allowance, though. It also performs worse if someone is coming over from or dualstreaming to Twitch, and thus still limits their bitrate to 6000kbps, but that's user error, not Youtube. This all assumes someone is watching Twitch using the Source output, of course. Else it all falls apart and Youtube is never worse, only on par or better.
Youtube also allows streaming at higher resolutions. I stream at 1440p personally, feeding it a 20000kbps NVENC encoded input.
As a viewer, there are also ups and downs.
If you are a passive viewer, who is just there to watch and not interact, Youtube wins outright. Ads are more easily blocked without a specialized adblocker that may or may not work.
The specialized Twitch ad-blockers haven't been working for me for months. I check occasionally, and just leave the site immediately when the pre-roll or a mid-roll ad plays. I don't understand how it working can vary from person to person, but no one that doesn't have issues seems to believe it's possible for it to not work. In my case I only ever really bother with mogra, ESA, and rtainjp, so it's not a heavy loss, and vods are still easily downloaded in the latter two cases.
If you are an active viewer, Twitch wins, no contest. Their chat is nice and slim, being an extension of IRC. There's also a lot of plugins streamers can use for viewer interactivity. Though I imagine some of that could be done on Youtube, it would just be a pain in the ass and break often, so it's not worth it.
Meanwhile, Youtube's chat is one of the most atrocious pieces of shit I have ever seen. You can tell whoever designed it expected there would never be more than 100-200 active chatters, chatting in a non-spamming fashion. The resource usage in ridiculous, and the data for each chat message is holy fuck bloated with unnecessary extra shit. I cannot blame anyone for being a Twitch-only fag if they actively use chat.
