Ross is the one that drives me insane. Literally every other person demonstrates some sort of growth over the 10 years the show takes place, but Ross is pretty much exactly the same.
For me, Rachel starts out annoying but gets more likeable through the seasons.
I was watching a few on a road trip and happened to catch them when Rachel was rejecting Joey, then demanding Ross not date and stay with her. She was just awful in every episode I saw.