Get off Aski.

As for switching clients, I started seriously considering this issue a couple of months ago, and even asked for the opinions of some users. Among the options, I considered Skype, Discord, and WhatsApp. The latter seemed not bad, but it was immediately rejected because everyone would have to essentially post their phone number online, which many are, of course, not ready to do, plus, as it turned out, not everyone has a smartphone. Skype, which changes with each version and not for the better, also didn't really please people. We even tried to create an HW channel in Discord, but that idea also failed. But with the death of QIP, the problem seems to be relevant again. Let's discuss what default messenger would you like to see as a communication tool?

As for Slack, at first glance, it seemed to me like the same Discord, only in a browser version. Maybe I'm wrong, but the system seemed very similar.

Ideally, it would be good to integrate a communication tool directly into HW, so that we wouldn't have to use something external.

Otherwise, I think that the default version should be something well-known, where everyone doesn't have to register or learn something new. I would suggest Skype. But I feel that people are so attached to ICQ that this conversation will end in nothing.

Personally, I don't care whether it's Discord or Skype. I'm against WhatsApp due to its strong link to mobile phones. Regarding Skype, in recent years, everyone feels a reduction in usability (for instance, the new client lacks convenient features), so I don't think moving there is a very good idea because it's just not a very convenient tool right now (and I suppose it will be less and less convenient eventually).
Regarding Discord, yes, it can be a very good alternative, so if everyone agrees on that, I would also agree.
Regarding the difference between Slack and Discord: they are actually very similar in their basic functionality. But their areas of interest are different. Slack is mostly used by teams and companies (usually software developers, etc.) because of its many integrations with different tools (build tools, website APIs, etc.). Discord considers itself a platform designed for gamers. So, it has a built-in TeamSpeak, integration with Steam, etc.
From a moving standpoint, we can use Slack (because the Creator has already created one), registration there is very simple and straightforward, and usage as well. We can also use Discord (in this case, you or someone else should create channels and other infrastructure for H3 gamers). It actually doesn't matter.

One more thing: in Slack, you can have the same nickname as in Heroesworld, which will simplify recognizing you by other players; in Discord, there might be problems (correct me if I'm wrong).

One important thing: in case of moving, we need someone who will create a manual about which can then be posted somewhere like "how to start communicating with H3 players." In this case, the transition will be easy and seamless, and everyone will be able to point newcomers to this post with RTFM.

Added 2 minutes ago
Update: thanks to the Creator for the clarification. If Discord is just a fork of Slack, there is no need to move to Discord specifically. Slack is a better alternative, I suppose.