I use a Playbook for streaming video with no problems. The Kindle Fire and Playbook both have hdmi out which means you can connect them to your telly.
If that's not an issue, and he's likely to want to do other stuff as well, the Samsung is a better bet (also the Google Nexus) as both the Kindle and the Playbook are largely tied in to proprietary ecosystems. In this respect, the Playbook is the worst of the lot, as the available apps are extremely limited, and expensive compared to the others.