I have a Smart TV that was given to me as payment of a debt. I like the TV, but after trying to get the smart features to work satisfactorily I ultimately gave up and plugged in my Roku.
The tv's smart interface and all apps are dreadfully slow to respond. The Netflix UI is terribly dated in appearance and functionality, and the Plex app wouldn't connect to my plex servers. I sideloaded a plex app from the deveoloper and this was able to connect to my servers, but stopped functioning shortly thereafter. The Youtube app was slow and pairing it with an android device was always a crapshoot.
The tv was missing a critical app for me, so the Roku purchase was inevitable, but the apps included with the smart tv are by no means a working substitute. If Samsung et al would actually provide a positive user experience with their smart suites then I would certainly be onboard. But in reality, much like SOHO router vendors who pathetically attempt to provide 'premium' features with their device firmware, tv vendors should stick to selling tvs.