First I was contacted by the HR staff. She was very professional, although it wouldn't hurt if she was a little bit friendlier. After exchanging some information, she decided to forward me to coordinator of the position I was applying for. He was very professional as well, it looked like he was in a hurry so there wasn't so much room for get to know each other better, but everything went ok. He sent me a theoretical problem to solve and discuss about it in the next round.
After that, I was forwarded to the tech interview round, with the same coordinator and other dev (team captain I guess). The team captain was the most friendly staff in this interview process, and the coordinator joined us about 15min later. I had to explain the approach I've used to solve the previous problem.
The coordinator seemed a little bit grumpy, and questioned a lot of concepts I chose to use. To be honest I felt uncomfortable by their approach, since they were a little bit aggressive, asking me questions out of nowhere regarding the problem (I think it was part of the interview, to see how you react to unpredicted situations, but again, they could be a little bit friendlier about it). In my opinion, they're totally entitled to evaluate me (or even criticize me, since they're the ones who are hiring), but I don't think it should be during the interview.
We had a little argument during the meeting, about technical principles and concepts but in the end, the coordinator let it go.
By the behavior of the tech staff, I thought I was done but surprisingly I was successful and received a nice offer. Since I felt little chemistry towards the coordinator (and even the recruiter herself) I turned it down.
My advice to the company is to be friendlier towards the candidates. An interview process is a game of seduction (the candidate seduces the company, telling them why he/she should be hired and the company seduces the candidate, telling him/her why they're a good company to work for) but you kind of acted like it was a one-way road.
To the HR: you're the first impression of the company, don't be so robotic when making and answering questions, and don't be so rude when complaining about the call quality or alleging how busy the interviewers are when the candidate turn down a proposed schedule.
To the tech staff (in this case, coordinator): It's totally fine to disagree or even dislike candidates, after all, you're the one assembling the team. But in my humble opinion, any criticism regarding the candidate should be done behind the curtains, when giving the feedback to the HR. Otherwise you will lose the candidate right there.