This really depends on their team comp. If they have a really tank heavy team go for LDR first but if they are really squishy you go for the IE

+ fastest wave clear I've seen yet
+ huge teamfight potential
+ strong late and mid game
+ good kiting potential
+ Featherstorm allows you to dodge everything!
+ stun

- weak early
- can't engage quickly (has to stack Feathers)
- lack of mobility

BOTRK gives you alot of sustain in the laning phase it has an inbuilt slow and some attack speed wich is good early to late game. If you woud go for a normal ADC build on Xayah your early game will be really bad and you will porbably have to go back alot because you wont have any sustain.

BOTRK Build Pros:
+ Good sustain in early game
+ Has an inbuilt slow
+ Allows you to get to the midgame power spike earlier
+ A bit of mobility

Normal Build Pros:
+ Good harass
+ Fast early wave clear