Riven or Fiora

Which of these two melee carries should I make my mainstream powerhouse? Our good old loved and hated Darting Doom's Day Dasher , or our newly rediscovered and reformed fencer ? Both of them have serious outplay potential and mechanics and, are lots of fun with high skill caps for certain. What I can't figure out though is who is more fitting to me.

They are similar yet different in a lot of ways, which makes it hard for me to choose. What do you guys think? Yeah I know it's my own decision to pick, but still some insight and/or pointers from others would help me out. Thanks.