Well the best would be the Xbox one S.... as it's the newest(a little faster, menus in 4k look a lot sharper). As for your LG TV, you need to find out if it supports HDR / BT2020. Just having 4K, as long as your TV supports HDMI 2.0 and has HDCP 2.2 you will be able to watch 4K Blu-ray and 4K videos on it (youtube, Netflix, etc).
The big advantage to the Xbox one S is HDR graphics as they are not true 4K, they do offer a larger level of color and most people who have used it say games look a lot better (the game needs to support it, limited titles now but, new releases seem to support it).
If your TV is 2-3 years old, you might not support the HDR / BT2020 meaning no HDR graphics from the Xbox one.. Something to keep in mind. But, still, you can play 4K Blu-ray (based on above) and being a Xbox one, so you can play the top games and still see some 4K content, so it might be worth it just for that.