There is a 3rd alternative...
Atolia, the one and only workspace your team needs
Atolia is a power-packed all-in-one digital workplace: Chat, Video calls, Tasks & Projects, Calendars, Documents, Notes...
Accelerate your team's collaboration game.
Implement it in minutes and save money. Atolia is cheaper than most of the business instant messaging apps.
Why choose Slack or Lark?
However, Slack offers more features including add-ons, graphic personalization, custom domain name, workspace and user activity, voice messages, poll, whiteboarding, screen sharing, and multiple workspaces. Meanwhile, Lark offers more storage options ranging from 100Gb to 1Tb, as well as document viewer, documents management, online document editing, search, newsfeed, notes-taking, calendar, task management, training webinars, dedicated CSM, mobile app, web app, desktop app, and data & users import.