What is the best KEKKEI GENKAI???

[Made in Heaven]

I don't think it's perfect, but Byakugan is what I like the most

 

[SasukeUchiha910]

Sharingan.

 

[ShinraTensei17]

Sharingan, Lava Release, Ice Release, Shikotsumyaku, Wood Release.

 

[Percy Jackson]

Rinnigan, and wood are the best!!

 

[Transcendence]

Anybody who mentions the Rinnegan is an idiot. It is neither inherited nor a combination of 2 elements.

As for what is the strongest KKG? Probably Mokuton. Sharingan comes close.