Use what you like best.
Smooth introduces way too much soap opera effect for me. Clear looks very natural with good quality sources. True 4K footage with Clear motion looks almost SOE-free except for fast-moving stuff at the edges of the screen, and stuff like fire where you can see some motion interpolation.
The advantages of True Motion vary wildly with different sources. I see this especially with User settings. Older movies start showing SOE with Dejudder set to 3, while I noticed more modern films look natural at 3 and start looking artificial at 4. Dejudder set to 5 will have SOE no matter the source.
Most people recommend setting Deblur to 10, but I can’t stand it if it isn’t coupled with some heavy dejudder.
I’d be interested in user opinions on the new Cinema Clear settings and BFI on the new LG CX. BFI is basically useless on the C9, I doubt even a giant CRT could flicker more than that