For what you posted at the end, Varus is probably better for you.
Vayne
To play Vayne to her highest potential, she needs correct positioning. If you want to struggle learning it, though, she is one of the best ADC's to learn it on, as messing up basically = death or harassed out lol. She has one of the highest outplay potentials, but this requires a lot of experience with her to pull off. She has one of the weakest laning phases of ADC's being able to get beat out by most matchups. If she is able to get ahead, though, she will easily be able to dominate if played correctly and she snowballs incredibly hard.
For Varus, he is similar I guess to Ez, but his Q is easier to land as it isn't stopped by minions, just its damage is reduced depending on how many champions/minions it hits. He has easy poke and one of the only two ADC's with an initiation, the other being Ashe. His "flaws" I guess you can say are he has no dash, so he requires good positioning because he has to blow flash to escape. Also his abilities (Q and E) have long CD's.
As a side note, I'm going to suggest other ADC's just for one aspect that they have that Varus/Vayne don't have. I'd suggest playing an ADC with a dash/jump, like Trist, Ez, Lucian, Graves, or Corki. I'm not sure if you own any of these, but I feel it will be less stressful for you to play as you won't have to possibly blow flash whenever the enemy ganks you and you are over extended or if you get caught out of position. Being able to have a jump/dash ability allows you to get away for "free" so it might make the experience funner/better for you.