SCROLL DOWN FOR THE TIER LIST IF YOU HATE READING. I'M SORRY FOR THE WALL OF TEXT.
HOVER EACH CHAMPION TO SEE WHAT I PERSONALLY RECOMMEND. EACH CHAMP IS RATED FOR SOLO Q EXPERIENCE DISREGARDING CHAMP SYNERGIES.
Edit: I may have been wrong on the "attack speed" ADC itemizations. Going full Crit with Hail of Blades is no longer the way for sure and Lethal Tempo AS builds work far better, but it seems that it's really just Kraken Slayer that's the outlier and after that it's more effective to just go full Crit again after building it (some exceptions). Need to test further and then fix all recommended if so.
As with all URFs, DON'T BUILD Boots unless you have Predator or if your champ REALLY needs them (ie. Zoomies Jhin or Briar sometimes).
I'll put a note if Boots are "needed/recommended".
Side note 3: In item recommendations, the slashes (/) don't just mean build one or the other, you can build both and definitely should if they have an asterisk (*). It's just a general guideline to build at least 1 item from each row (* = build one of these before moving on).
Side note 4: Anything C tier or above can carry games. You don't HAVE to only pick S tiers. Have fun with the mode, try it all out.
Best of the Best
Low A, still A though
Barely benefits from URF buffs
IDK but most likely A or higher, maaaybe B
Like I know these champs are good, they're just in untested/unseen limbo