When comparing Telegram vs Flock, the Slant community recommends Telegram for most people. In the question“What is the best team chat software?” Telegram is ranked 3rd while Flock is ranked 17th. The most important reason people chose Telegram is:
Copy/paste videos, gifs, images, geolocation, documents, and even executable files. Drag over files for practically any time up to 2GB in size. Images can be compressed, too.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Free and convenient large file sharing
Copy/paste videos, gifs, images, geolocation, documents, and even executable files. Drag over files for practically any time up to 2GB in size. Images can be compressed, too.
Pro Free of cost
The application is available free of cost.
Pro Privacy focused
In addition to the end-to-end encryption [only in secret chats] that provides privacy to communications, the app also includes self destructing timers for chats, and the ability to permanently delete messages, yours and theirs, from your and their devices.
Pro Media messaging
Videos, gifs, images, geolocation, and documents.
Pro Channels for one way broadcasting
Broadcasting channels suitable for announcing things.
Pro Beautiful UI
Very customizable with a lot of clean looking options.
Pro Possible to send photos and videos without compression
Pro Supergroups of up to 200,000 people
In Supergroups, anyone along with admins can delete their messages from all sides. A message can be pinned to the top. All of the user's messages can be deleted by an administrator, and they can be banned and reported as well. Supergroups can have a public link (outside of Asia, due to high spam volumes), which is also a username.
Pro Two-step verification
You can set up an additional password to your account, which can be reset by your email. You don't have to use an email if you do not want to. If you lose access to your email or forget your password, you will be able to reset it via text message if your account is over seven days old and will receive it within a week (in case you recover anything before then).
Pro Secure
Pro Saved messages
You can write messages to yourself. You can write some notes, add links, and see everything across all your devices.
Pro Cloud chat keys are kept in different jurisdiction
Even though encryption used for cloud-based storage (e.g. Gmail, Facebook, iCloud) may not be as secure as end-to-end encryption or zero-knowledge storage, Telegram does the most that it can by holding keys to chats in different jurisdictions, requiring intergovernmental cooperation to obtain the keys. This is aside from whatever other security measures have been taken, of course.
Pro Multiplatform native client apps
There are native desktop, mobile and web client apps, that are optimized for speed and are light on memory usage.
Pro Open source client apps
Client apps are open source, making whole service more trustworthy.
Pro Unlimited storage
Unlimited number of files can be stored forever on the cloud. You can upload files up to 1.5 GB each.
Pro Voice and video messages
You can post voice and video messages if you are too lazy to write text messages.
Pro Group Voice Chat
This Discord-like feature adds to the interactivity of the application.
Pro Pinned Messages
You can pin messages to the top of groups or supergroups so members will see them when opening the group.
Pro Self-destruct messages
Messages in individual chats can be set to self destruct on a timer. They will disappear after the timer expires.
Messages in all new chats can be set to self-destruct with a global auto-delete timer in Settings > Privacy and Security > Auto-Delete Messages.
Pro Edit or delete messages after sending them
Pro Banned in China
Pro Save time with inline bots and link previews
Unfortunately, on the desktop videos don't play, but images are viewable without visiting popular websites like imgur and Instagram.
You can play YouTube videos and others within the app, so you don't need to embed code or anything.
With inline bots, such as @gif, @pic/bing, @vid/YouTube, etc, you can look things up without leaving the client or chat that you're in. Simply type the name and some keywords and wait for the results to load.
Pro @mentions
You can ping people to get their attention by @mentioning them.
Pro Desktop app handles HiDPI
The desktop app has a built in setting to scale the UI of the app up to 200% which allows for those with 4k monitors/screens to use the app without scaling issues.
Pro High quality calls
Uses the latest GPL audio codecs, such as Opus, an adaptative high-quality codec that supersedes AAC at any bitrate.
Pro Customer support is within the app
Although it's volunteer based, but still pretty top-notch if available, which it tends to be.
Pro Large groups can have channels called 'Topics'
Topics are now available in groups of 100+ members and have a sleek two-column layout and new buttons to quickly navigate.
A default topic called General is now in every topic group, holding the group’s service messages and previous message history.
Pro Popular in the USA
On SimilarWeb you can see that Telegram is on the top 15 among all communication apps.
Pro Cross-platform
They have apps for Windows, Mac, Chrome, iOS, Android and web interface. And all the chat sessions are always on sync.

Pro Clean and clutter free interface
Pro Cheaper than Slack
It is half the price of Slack and full of nice features like polls, assign to do's, etc.
Pro Very powerful integration APIs
Unlike its rivals, it not only allows you to receive events, but also allows you to push content to it and receive various user action events.
Pro No IT team required for setup
Moving a team or organization to flock does not require any setup from the company's IT team. At max, what might be required would be to whitelist their domain in case the organization's IT team has gotten external domains blocked. You can simply download Flock and invite others in your organization by using their email ids in order to start collaborating. That's all there is in the name of setup.
Pro Free if you don't need the most advanced features
Most of its features are free, even video conferences. But also they have a Pro version with unlimited chat history, Active Directory integration among other things.
Pro Unlimited groups and teams
There is no limit on the number of groups or of group members. Similarly, within a team you can have unlimited members. There is no limit of number of teams too.

Pro Faster than Slack
Flock is offering an app that is faster than Slack.
Pro Highly configurable permissions
For every team, the permissions and restrictions can easily be set over the participating members and the conversations they are having.
Pro Better than slack
Pro Stickers
Posting messages is more fun with them in addition to emojis.
Pro Customisable UI, integrations surface just like native features
There are multiple options like slash commands, message buttons, chat buttons, attachment picker etc., where the integrations can surface inside the native app. This greatly eases the discoverability of a integration, making it really easy for the team members to find and use the integrations.
Cons
Con Not fully open source
Telegram has an open API and protocol free for everyone, but the backend software is not open source. Therefore 100% privacy can not be evaluated.
Con Can only be used with a phone number
It is not possible to activate and use Telegram by mail etc. You need a phone number.
Con Only "Secret Chat" messages are encrypted end to end
The only way to get end-to-end encryption (client-client) using Telegram is to use the Secret Chat function, anything through the service is server-client encrypted. Also secret chat is only implemented in the mobile apps, meaning there is no way to encrypt messages end-to-end when using the desktop client or the web browser client.
Con "Secret Chat" feature is not available for desktop client
Secret chats with end to end encryption are only available on mobile apps.
Con No source code sintax highlighting
Telegram does not have source code syntax highlighting, making it difficult to share code snippets.
Con Does not work for visually impaired
Doesn't work for visually impaired.
Con Does not support spherical 360° photos
Spherical 360° photos becoming more popular these days, but Telegram does not support such format.
Con Does not support text messaging
You can NOT make it your default text messaging App.
Con No thread feature
Reply command only quotes snippets. There's no implementation to show thread(s) of an initial message.
