For the best quality and selection of videos, running your own automated media server with Emby, Radarr, Sonarr and other associated programs is the way to go. That does require some technical knowledge and regular maintenance though; the following apps are a good alternative if you don't want to invest the time, or if you want a simpler setup for a family member or friend. I may make a guide for setting up an automated downloading & streaming server in the future.
Hardware
The best streaming device by far is the NVIDIA Shield. It retails for $200 but goes on sale from time to time for around $140. It has a fast processor and plenty of RAM, so you won't experience slowdowns as you would on cheaper devices.
Cheaper options include the Mi Box S ($50) and Amazon Firestick ($40)
Services
Trakt.tv - This syncs your watching progress across all the apps. It's free, and pretty much essential.
Real-Debrid - Debrid services cache the videos from the various hosting providers, and provide much higher quality and more reliable streams. It's not strictly necessary, but you will get much better results using a Debrid service. It's 9 Euro for 180 days which comes to about $3.30 per month. Note: You can use this on as many devices in your household as you want, but if they detect multiple IP's at the same time they will freeze your account, so best not to share with your friends.
Apps
Since many of these apps are modded, closed source, and from questionable origin, I wouldn't personally put them on my phone or any device containing sensitive information.
To install apps outside of the Play Store, you need to enable unofficial sources by going to Android Settings > Security > Check to allow Unknown Sources and click ok.
Installing apps on the Firestick is a little more involved, there is a guide with pictures here: How To Install and Use Downloader App on Firestick
X-plore File Manager - File manager which works well with the Android TV interface. Use to copy files / install apps.
MX Player Pro - Standalone video player for Android. Most streaming apps have their own built in video player, but often times they are less reliable and use more resources than MX Player. I recommend the latest [Patched/AC3/DTS Ultra Mod Lite] version by Balatan, which unlocks pro features and removes all ads and telemetry. You can get this by searching forum.mobilism.org (you need to create a Mobilism forum account to search).
Streaming Apps
Ah, here we go, the good stuff. There are tons of streaming apps out there; I'm just going to list a few that work well for me.
Cinema HD - This is my go to app, it has some of the most sources and generally works really well. It has ads by default, since I hate ads I pay for the ad-free version which is $5 for 6 months and works on 5 devices. It requires paying with Bitcoin. You can also find a modded / ad-free version on Mobilism, but it breaks with each app update and is generally not worth the hassle to me.
TVZion - Another great streaming app with many unique features such as automatic source selection and next episode autoplay. It also has ads, which can be removed in addition to other premium features by subscribing to Zion Club which is $6 for 4 months and 5 devices. Again, you can find a modded version on Mobilism but it's so inexpensive that for me it's not worth the trouble.
CyberFlix TV - Decent streaming app, I don't use it as much as the others but it's good as a backup and will sometimes have content that the others do not.
FireAnime - Anime streaming app designed for Android TV
Other Resources
VirusTotal - Online virus scanner, use to scan downloaded apps
Mobilism Forum - Forum for cracked / modded android apps
r/TTVReborn - Subreddit for streaming android apps
r/ApksApps - Subreddit for modded streaming apps
/r/moddedandroidapps - Subreddit for (go figure) modded android apps
/r/Addons4Kodi - Unofficial streaming addons for Kodi. I don't personally use Kodi for streaming anymore, but it is another option
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