Let me put it this way...
You have to play strategically with your team mates.
Everyone has a team lineup...an 90% of the time you're going to find nothing but the most OP'd tanky champs in your ranked opposition.
With that in mind, you also have to keep in mind that some people will play the Burst Dmg champs over a tank because hey, lets face it...if you can't tank or deal damage in ranked ~ you're pretty much worthless...or at least that's the attitude from season 5.
This season, I've been seeing A LOT of JG and ADC builds like Katarina, Tryn, Veigar, Riven (seems to be used in EVERY season) and a few select other burst type champs in various match-ups.
I spectated a match with the following 10 champs:
Versus

Who do you think won this match-up?
Most Kills?
Most assists?
Who Sucked? (Most deaths)
Not a trick question...this match lasted over an hour.
Personally, I would go with
all the way, because if you don't lead the charge with her, you can pretty much ensure that your team will succeed with the Oppressor mastery. That extra 2.5% damage dealt to disabled champs is one of Quinn's strengths early and mid game.
Quinn's slow and blind can make a huge difference in team fights or picking off a Would-Be gank by the JG.
Think about that for awhile. Quinn's squishiness is out-weighed by her ability to pick off just about anyone that lacks ranged attacks or a feasible means to disable her.
EDIT:
....I love this champ, but if you're team absolutely refuses to feed you or assist you early on, you'll be a hindrance the entire match. Twitch's greatest strength comes from his burst attack rate once outta stealth, and the ability to slow his prey...and lastly, his Ult. Other than that, I'd avoid twitch unless you can get fed VERY early in the match...as you're going to struggle making the game changing gear you'll need to rip apart the tanks and ap builds...forget the tanks, even with 60% Crit and IE's 50% crit damage...tanks will brush your damage off, even with
and
.