League of Legends (LoL) Question: Best Adc in this meta And the best build ?

There isn't a best adc at the moment, different ADC's excel in different things. Sivir for massive late game AOE damage, Jhin and Lucian for their superior laning phase (though both offer different tools late game), Tristana for sieging, Ashe for long range pick potential.

I wouldn't worry too much about meta. but that's just me. depends on what your trying to do jhin is a late game beast as well as sivir, twitch (main) and Jinx (secondary). Ashe is great for initiations with her ult and can kite very well if needed. trish has a hard early game but late game is the siege queen.