Jeff has great bandwidth - 100Mbps down - but when he's streaming on his TV, he gets constant buffering. Leo says that smart apps on a TV are terrible. So Leo advises avoiding them and going with a streaming box like the Roku. Jeff says it's also happening with the Fire TV, though. Jeff is mostly having a hard time streaming DirecTV content. He has a SWiM box which is connected over the LAN in his house to his DirecTV receiver. There shouldn't ever be buffering, so Leo thinks it's the SWiM box. It is possible for an ethernet connected device to bring down the whole network by spewing packets inappropriately.
Leo says he should slowly eliminate the easy things like replacing cables. Since streaming to mobile devices is fine, then there's something localized like a TV connection. That's where he'll want to start troubleshooting.