Corki or Vayne?

Which champion should I buy when I have enough? Some backstory to help with the decision: I suck at ADC mostly because I haven't invested in a solid pick yet. These 2 champions are the ideal picks for me, Corki has a solid repositioning tool, reliable true damage, and excellent poke. Vayne's mechanics are well known, she has been known to 1v5 full build teams that forget to buy pinks when she has all of her cds up. This will need to be my main and only ADC while I save up for the other one, so I will let you know something weird about myself: I need to be able to trust my champion to pull through for me. I want to be able to rely on the champion itself to help me carry. I will take a reliable champion who helps me pull through a very large variety of situations over an unreliable champion that only makes plays when snowballed (consider my main's Nasus and Akali, no matter how far behind or ahead I will always know EXACTLY what my champion can and cannot do if I'm paying attention). So ADC mains out there, which champion do you feel you always know what you can pull off with, Corki or Vayne? P.S. I will be heading into the fearsome world of solo queue ranked after I learn the champion I buy, so if it's a tie for you please vote for the champion that's a stronger solo queue carry. If you voted for other please leave the champion you think I should get in the comments, and up-vote your favorite if you already see it. And thank you for reading this seriously long thread, have a good day and God bless!