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 Basecamp or Flock?
Basecamp offers graphic personalization and custom domain names, with roles management and contact management as well. It also has features for workspace and user activity, chat, file sharing, mentions, and groups/channels. Flock, on the other hand, offers a free version, polls, and 1-1 video calls with up to 20 participants in group video calls. It also has screen sharing, audio calls, and "Do not disturb" mode, with help resources including training webinars and a mobile app.