Overwatch. It has its share of toxic players, but it has a significantly much less toxic community compared to League's, because the incentive to not be toxic is monetary: People have paid money to play the game, and if they get banned, they just wasted $40-60. The threat of wasting money (or their parents' money) is enough to keep a good chunk of the community to check themselves before they wreck themselves.
If you want an RPG, go for FFXIV. I've only heard good things about the game from both the actual game itself, and the community. I guess it's because people pay to play the game, and getting banned is enough to keep people wary about not being enormous jerkwads to each other. It's not a MOBA, but it's definitely a game I would like to pick up when I do get the money saved up to do so.
Mobile Legends. Literally a mobile version of League, but the good thing about it is that there is no voice chat, and people spend more time playing the game rather than trying to make others feel like crap. It's a Chinese knock-off (literally) of League, but it's a good knock-off that I find myself playing every once in a while when there's nothing to do, or to kill time.
I've noticed that I've had to report at least one player in every single one of my games since I made this account. Most are bots, but the ones that aren't bots are people like that in the screenshot. It sucks, but I seriously think that there are more bots and toxic people in this game rather than nice players as a result of how frequently I have to report a player or a bot.