Rick cut the cord about a year ago and he streams using YouTube TV. Leo uses it too, but at $50, you're not really saving anything. Especially when you spend money on HBO, Netflix, etc. But their DVR capability is great.
While Rick likes YouTubeTV, it buffers constantly in the evening. The only way to stop it is to switch channels and switch back. The other services don't do that. He uses a Roku. Leo says that it may well be that the YouTubeTV app on Roku just isn't very good. Likewise, AppleTV's app on Roku is awful. So it could be that the app just isn't written very well. Also try deleting the app from your Roku and then reinstalling it could help.
A faster processor in the next level Roku could help. There's also the fact that YouTube uses the new VP9 streaming codec, and Roku may have a challenge decoding that. Rick could try getting a Chromecast and see if it works better. Leo suspects that since Google makes Chromecast, YouTube TV will run better. It's cheap at $45.
From the chatroom - The HDMI cable may be the culprit. A new HDMI cable may be made with the updated standard and that could help. Switching to a hardwired internet connection directly to your router would also help. It reduces the congestion of WiFi. That would be an ethernet connection.