Gangplank or Fizz

Fizz is most a mid laner while GP is a top laner, so there's also that.

This is if you're disregarding stereotypes.

both can be played top and mid, play fizz if you want everyone to hate you (even teammates) and play gp if you want to get all the money

Personally i'd go for fizz

gp is probably going to see even more nerfs down the line to the point where he should be the next better nerf irelia joke.