I've used both. Ruku is fine, but kinda limited. Sling was terrible for me. I constantly had audio/video sync problems.
The best streaming service in my experience is playstation vue.
You don't actually need a playstation to use the service, just a playstation network account. After that, you can access PS vue on roku using the PS vue app.
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No man is free who is not master of himself.~Epictetus