I've played rude people from all over the world. It's the internet - a place where common courtesies go out the window.
Who are the most friendly players?

Maybe. Hard to know. I prefer someone who does not communicate to someone who writes insults or tries to provoke you to lose your concentration.

1. The Americans are always friendly and polite players. The write GG, wishes a good day, congratulate etc. Some times we chat a little afterwards: talking about mistakes, the weather in USA and Norway etc. It is fun! I like to play with Americans.
That's right, that's the culture. Friendly superficiality. But friendly. I like to play against them.

GM Yasser Seirawan, is arguably the kindest chess player. If you've seen one of his lectures, he is always so calm and open to suggestions and questions. He is also known as the Bob Ross of chess.

There are nice people in every part of the world. It does not mean they play chess. The opposite is also true.

Normally doesn't occur to me to message people I'm playing, even with the completely banal and vapid gg. There's a balance between wanting to be thought friendly and not wanting to be thought a boring idiot.
I have played against Alexander Shabalov in an OTB tourn, lost of course but he was very friendly after the game and seems to be a friendly guy from the other tourn I have been to where he was playing!

GM Yasser Seirawan, is arguably the kindest chess player. If you've seen one of his lectures, he is always so calm and open to suggestions and questions. He is also known as the Bob Ross of chess.
but nice guys never make world champion, unless your surname is Spassky.
You are right, Schlechter is an example.
But nice guy can be No. 2, thats not bad..
I have now been a member for a couple of years. I play daily, most for fun: a win and loose. However, I see that some players are better winners (and losers) than other based on their nationality. Here is my ranking:
1. The Americans are always friendly and polite players. The write GG, wishes a good day, congratulate etc. Some times we chat a little afterwards: talking about mistakes, the weather in USA and Norway etc. It is fun! I like to play with Americans.
2. The worst players are those who come from The Middle East. They abandon the game and they NEVER write GG. If I write GG, they don't answer. Why are they so unpolite? I can't understand it.
My fellow Norwegians are medium, I would say, as most of the nationalities.