My samsung tv has those free live channels too, but I wasn't impressed with the offerings. Plex live tv seems decent mostly because they have an entire channel dedicated to Bob Ross. You can watch Bob Ross paint 24 hours a day. btw, plex also has free movies on demand with ads. Vudu has free movies with ads to but I haven't used that app in a while since I have most of my digital movies all on my plex server.
I haven't heard of tubitv until your post. lol. I'll look into that later to. My brother and a friend of mine both use the Kodi app to stream movies and series but they both say its a bit hit or miss, probably because I think alot of the kodi stuff is all pirated movies but the different servers or addons keep getting taken down. Something like that.