Streaming video games is quickly becoming a very popular past-time and a way to get others involved in what could otherwise be a solitary activity. This can be done with more than just PC or console games: it's possible to stream Android games in myriad ways, and some services allow you to stream natively from your device without a capture card.
If you have an Nvidia device, you can stream natively to Twitch from them, but, otherwise, you'll need a capture card in order to stream. Twitch's attempts at an API fell flat on their face, as very few games supported it over on iOS, and they have yet to introduce an Android app with streaming capabilities.
Using a capture card isn't inherently a bad thing, but on Android, it's a problem because not all devices have HDMI outputs through an HDMI port, MHL, or SlimPort. As well, some devices have to deal with HDCP issues – the Nexus 4 had this issue back in the day.
Also, Twitch runs into the issue of the stream delay. Essentially, streams are delayed by long enough that it makes it difficult to respond to people in chat in a timely manner, as a number of seconds have passed before you respond to what they say. Twitch is a reliable standby, but it shouldn't be the last place you look to stream your gameplay.
Google's official streaming service has a very capable Android app that lets you browse all your favorite YouTube streamers and games to watch them live. And streaming is very handy, too: you can use a popup on later versions of Android to stream games as you wish. While streaming directly from Android is not yet perfect, Google's solution is perhaps the most stable and functional that you can get so far.
It does run into an Android-specific issue, though: in order to record game audio, you have to crank the volume up on the speakers so that the game volume is picked up by the internal microphone. There might perhaps be solutions through mixers and external hardware to mix in-game audio and any external microphone, but it feels so oddly low-fidelity for an official Google solution. Perhaps later Android versions will fix this issue, but right now, you're not talking about the classiest streaming experience.
As well, YouTube Gaming is still kind of an upstart as far as streaming goes, and it's a console/PC audience. Mobile gaming perhaps has a bit more of a footprint because Android streaming can be done, but it might be an odd mixture between having a strong audience and not. The app is great and might convince you to use it just because streaming from it works the best natively from Android.
This mobile-exclusive streaming service is extremely promising. You have an audience that wants to watch mobile games, some top streamers stream regularly on the service, and the service performs quite well no matter how you use it. The problem right now is that the app to do more than just watch streams is currently not on Google Play (nor is it on the App Store).
As well, streaming is still very much in beta – even the capable and near-stock Nvidia Shield K1 has stability issues. And if your Android device doesn't support streaming, there's no capture card backup at this time. There are still some steps that Mobcrush needs to take in order to become the dominant home for mobile streaming, but it's got potential.
They were one of the first services to do gameplay recording, and have pivoted into mobile gameplay streaming as of late. They offer an Android app for live streaming and were ahead of Mobcrush in releasing it for Android, though Mobcrush was doing live iOS streams before Kamcord was. Kamcord, however, provides a streaming key, so you can stream through a capture card and software like OBS or XSplit, or even by using a remote mirroring server on your computer.
Which to use between Kamcord and Mobcrush? While it's certainly debatable as to who's drawing bigger numbers – neither Mobcrush nor Kamcord are necessarily drawing the massive kinds of audiences that popular games and streams can get on Twitch, for example – it's kind of the user's choice as to who to go with. Kamcord has a few more options, but Mobcrush's app might work better, or the community might be preferable there.
You might prefer the one-like-per-stream of Mobcrush, or like Kamcord's Periscope-esque hearts. Honestly, it comes down to user preference, and trying out both is recommended.
Smashcast, formerly Hitbox, doesn't necessarily have any mobile-related plans going that they have made public, but they're worthy of note if you have a capture card because they suffer from minimal stream delay. This is valuable in talking to a community, because you can actually respond to chat in real-time, as opposed to the stream delay that many services use. If you're focused on performance and that factor is key to you, Hitbox is perhaps a service to consider.