If you have Amazon Prime, then the Fire Stick is a no brainer. As far as performance goes, the fire stick is better as well in my experience. However, it doesn't have as many apps (or channels if you will) as the Roku. But since you can Airplay, that shouldn't be an issue for you because anything you can't get on the fire stick you should be able to get on your phone if needed. The fire stick does have all the main apps though.

I don't have Sling TV - so I can't speak to the performance of Sling TV specifically.