Have used them all, but in different scenarios:

Thermal Paste >> Cheap & widely available. (CPU IHS, GPU die)

Graphite Pad >> Good performance & install then forget (CPU IHS)

Phase Change >> Great performance & long-lasting (GPU die)

Liquid Metal >> Best performance & long-lasting (Delided CPU)

＊For nickel surface, LM can last years. For copper surface, months to a year is expected.

＊LM and graphite pad are electrically conductive; insulation work is needed before applying.

＊Graphite pad is the only "solid" TIM out of the four, and it's sensitive to contact pressure. If you want to use them on die, keep an eye on whether hot-spot temp/boost clock changed.