Depending on of you are A busrst OR An atackspeed adc. You take press the atack on Burst adc's like xayah and lucian. And you taken lethal tempo on Champs like kogmaw and Twitch. Only in a few situations you should take fleet footwork like in a vayne VS caitlin machupp
It really depends on the ADC. Most ADCs will take precision. I have personally found that Press the Attack works well on champs Sivir and Ezreal (thank god ezreal is an adc again), and you would take Lethal Tempo on champs like Tristana or Kog'Maw.
As people have noted, most ADCs benefit a lot from the Precision tree. I've been trying Domination ( Electrocute) on Tristana with Precision secondary lately and that's helped me a lot with her burst damage. It's also a lot of fun to take Sudden Impact. (But that's specific to Tristana).
It also lets me light up the map with Zombie Wards ;) because support vision instincts never die.
hope this helps,
~moon
It also lets me light up the map with Zombie Wards ;) because support vision instincts never die.