Most MOBAs are pretty notoriously bad, though Heroes of Newerth was definitely the worst one of those i had played.

Anecdotally, my personal worst experience was with FFXIV, which was probably exacerbated by how much praise that community gets otherwise. The Novice Network system they have is a mess, new players are put into a channel with a bunch of "mentors" that don't really want to help anyone, at least on the server I was on. They either wanted a global chat channel for their own use, or just wanted the cosmetic rewards mentors had on offer. I remember one actively trying to get new players to quit if he found out they had come from WoW. The channel is entirely self-moderated, and mentors would kick people out just for fun. It's an AWFUL first impression for newer players.

One thing WoW definitely does better with their Guide channel is giving literally no tangible rewards to guides, if somebody is opting into being a Guide it is only because they want to help new players, they get nothing else for it.