Simple. What champion should I get next? Mostly looking at either Graves or Quinn, but I'm open to other suggestions :p I'd get Quinn in a heartbeat but she has... problems. Graves is a strong ADC and he's pretty fun and has significantly less problems so.
If you're getting Quinn, get her knowing she's not an ADC, she's a fighter/assassin with an ADCs range.
Play her as a top laner, jungler (my preference, she's fantastic in the jungle), or even mid laner and you can excel. Trying to force her to be an ADC when her kit doesn't support it is why people think she has "problems". The only reason people insist she's an ADC is because she has range most of the time and Riot says in her profile that she's an ADC.
If you tried to force Nasus into being an ADC he'd have problems too.
That said, if you're looking for a strong ADC for bot lane, Draven and Graves are great. Quinn's a jungler or top laner.
For the current meta, go ahead and take Graves. High burst, good utility, a dash/attack speed steroid, and inherently more tankiness than any other marksman thanks to his passive. There's nothing wrong with Quinn from a theoretical standpoint, but she still has some nasty bugs and is trickier to play than most.
But also, it's more fun to pick champions that aren't as popular. If you want to have more fun with cool plays, pick Quinn.
I'd say 
, sure she has some issues and is lacking as an AD Carry, but you can take her Top-Lane and dominate if you don't want to ADC
Quinn's a ton of fun to play and rather underrated. As long as you're not trying to go Plat, pick Quinn.
Graves is probably my favorite ADC honestly, because to me he feels a lot more like an AD caster in most cases than an actual AD Carry, and I like that. He can dash in, blow all his spells, and if he doesn't immediately blow someone up, he can get pretty close. He excels in extended trades as well thanks to his passive, and his dash giving extra AS. He's a good ADC all around, and if you're at all interested in the ADC role, I'd say you should definitely pick him up. Also, he's a fun ADC to try and take mid-lane thanks to his heavy burst potential against squishy mids, which is always fun :D
Keep in mind, I'm terrible at League, and spend most of my time playing ARAM, instead of say, Normals, or Ranked, just as a warning that my advice may not be the most useful, or accurate.
my favorite ADCs are 
i found 
to be fun to play but she takes some getting used to.
between the two you asked i would go with 
, he fits a bit better in the meta right now, good burst, good dps, and gets tankier through teamfights which means he is a bit forgiving if you get out of position for a moment.
Jinx, Vayne, Ezreal,
because people play alot and no one plays people know how to counter-play but not . That's why I like 
.
