I kinda agree with CSZHUNG up there, and yes Tristana has to many AP ratios for an ADC as well as miss f i think.
And btw Vayne is an awesome ADC, you maybe don't see her a lot cause she has this huge learning curve, but, there are other champs that would actually benefit from a little buff or popularity, but it's all about the hype.
Graves, Corki and Ez are there not only for burst (if you go for burst go for Varus, kog, Vayne) but because of the scape mechanism and the traits each offer: Ez has the long range with no need to buy crit % items and a AS buff/debuff. Corki has that 6 second poke and the true damage and Graves is one of the tankiest adc because his passive is just really great.
I would love to see a Draven player on a tourney, but, his playstyle is really hard to pull off on a match the smallest detail counts pretty big, you need to catch that axe, and if you're good, axes.
Kog needs alot of positioning and early game farm without being harassed.
Vayne needs the farm, but, the ability to know how to engage, you need to be able to react, predict and kill in a second.
Varus is mostly practice iguess, stacking up his w and setting up either E o Q.
Sivir needs alot of mana management and the only moment its likely to see her would be against ez or corki to use that shield and block ez's q or corki's R, and stuff like that.
Ashe has no real escape and you need those smart choices.
Trist needs to get those AP ratios out and turn em into AD so she can scale well and be a more viable pick.
Teemo adc needs to be stopped being picked as adc by trolls and be picked by people that can actually pulled it off.
That's my opinion at least. =]