I used Sling for a couple of years and recently switched to Playstation Vue - much better.
I have a media room with a 55” flat panel and Amazon Firestick. Works great!
In another room, older 40” fp with Roku and Apple TV. Rarely use AppleTV (latest) as it is really flaky and hard to sync with anything. The V1.0 Apple TV worked better even if more limited.
Using Harmony to integrate all of these and use Amazon HD8 Fire (hacked to support Google Play apps) as a controller.
I have the latest Apple TV along with a Roku 4.
Both work great.