Hands down, it's portuguese. I've studied Spanish, French and Portuguese. I found french extremely hard to practice and I never was able to find reliable partners. Spanish was awesome and I found tons of language partners. I thought they were the best until I started studying Portuguese. I use Tandem and I talki and whenever I put that I want to practice portuguese as my status, I get 3-4 reposes within a few minutes. Plus the people that I meet are very interesting and extremely nice. They bend over backwards to help me out. So although I haven't practiced with anyone from Russia. I will say that out of my 3 languages, the friendliest language partners are as follows:

1. Portuguese

2.Spanish

3. French

Although, Spanish parters are amazing and I've developed very good friendships with a few of my spanish partners. They are always there for me. 

I've only learned three languages with language partners (the others I learned either in the country, either with teachers)

From best to worst

1 Indonesians

2 Russians

3 Dutch

Damn, one of the reasons why I stopped learning Dutch without speaking it well was the difficulty of finding language partners. People just didn't answer my messages and when I talked to them, they were so cold and unfriendly, didn't smile, didn't laugh, they were so formal. They are such an awful country.

Indonesians (and asians in general) are one of the friendliest people on earth!! They are so happy that someone wants to learn their language and talking to them was really easy. I spent seven months learning it and I got between two and three requests a week 

Russians are also nice. I made many Russian friends here, mostly women (I'd say at least 80% of Russians on Italki are female). They often reply my messages and it's fun to chat, we talk about many things. I spent most of the time speaking Russian because they don't speak other languages well

Thank you for saying that, Justin. I think it's probably because Portuguese is not as popular as French and Spanish. The problem of French is that is there are very few native speakers (only 75 million, compared to 470 of Spanish) and too many people are learning it (more than 200 million). So, French has more foreign language speakers than second and first language speakers combined. It's so ridiculously popular... 

Suppose every language partner has his preference according to their attitudes to the language learning, so I do not think there is a universal standard to say which country language partners come from is better than others. I know some language partners prefer to make friends, tease or even flirt to practice languages, but for some earnest learners, that might make nonsense to practice as they wish to have good progress in the talks and learn more from practice.

I prefer to select language partners who have concrete plans to practice and learn with no reference to where they come from.