As a person whom has built telegram, slack and teams bots.

Telegram is definitely not the worst, in fact, it's the best on that list depending on what you want to do.

Slack's real-time API has been deprecated since forever, leaving you only specific slash commands that hit web hooks, which does not allow for rich engagement of content or anything close to being as dynamic as the old IRC bots used to be.

Teams is a joke when it comes to bots. Seriously.