For me it used to be Dota 2. A versatile game with a strong competitive element. While playing with friends I got a hang of it and while in low ranks I developed a taste for team communication. In time even participated in a few tournaments. But as I kept going the more I understood just how complex and toxic the community is. It didn’t bother me that much, after years of verbal abuse and shouting I got used to it all to an extend. After my ambitions died down I stopped playing it as frequently as I used to.
Also the game is rather unkind to newcomers. The few actually new players that I encoutered always played with smurfs and angry low-skill players expecting everyone to know all the basics. On top of that a multitude of complex elements makes it hard for a person to get accustomed.