This comparison table mainly focuses on private use cases. For business group chat solutions please refer to Comparison of Google Hangouts Chat, Slack, Cisco Jabber, Skype for Business, Telegram, WhatsApp and other group chat solutions.
|Everyone has it||VERY HIGH||It's the only relevant upside of Whatsapp. Everyone has it. In almost every other aspect it sucks. See below to find out why.|
|Incredibly fast loading times||UNRIVALED||GOOD||VERY HIGH||While I have to admit that Whatsapp is fast, Telegram is simply much faster. Especially when I have poor web connectivity I often experience much easier handling in Telegram than in Whatsapp. There is nothing more important than speed for messengers.|
|One account multiple devices||VERY HIGH||If you have two smartphones (business and private) you will need to run two Whatsapp accounts. That's very inconvenient. In Telegram you can use one account on all phones, tablets and desktop computers.|
|Fast sharing of pictures||3 CLICKS||5 CLICKS / 3 CLICKS||VERY HIGH||Whatsapp is confusing as it offers two ways to share pictures. The most prominent way is via the "+" icon:This way takes 5 clicks on your smartphone. That takes much longer and is more confusing.|
|Zero upload picture forwarding||VERY HIGH||Every picture you have sent to Telegram once (e.g. to your spouse) can be easily shared with unlimited other groups (friends, family) without additional uploads. That is much much faster and saves expensive bandwidth especially if you are abroad.|
|Searching in all conversations||VERY HIGH||Telegram allows you to search in all messages and media. That is very handy.|
|Offline abilities||GOOD||OKAY||HIGH||Sometimes you simply have no connection and your video or picture cannot be transmitted. Telegram handles such situations much better then Whatsapp, as it offers drafts, highlighting of unsent messages, and offline storage for not yet transferred content. Unfortunately neither messenger has an auto-resend feature.|
|Native desktop client||HIGH||Telegram has a fast and slick app for all smartphones, for Windows, Mac and Linux, and a cool web version. Whatsapp is mainly for your smartphone. Telegram saves time dramatically in all situations when you have a real computer at hand. Since April 2017 Whatsapp has a Mac client. But it still relies on the smartphone being present and switching between Mac devices still needs QR code scanning.|
|Easy access for multiple devices||HIGH||After initial security screening via code verification, Telegram is seamless across all devices. Whatsapp is cumbersome with always asking for re-authentication on devices via a QR code.|
|Privacy and Data Security|
For Telegram: the service seems to be very secure and did not show any vulnerabilities or weaknesses in the past. Problem is, that you have to trust the owner and his team to be trustworthy. Normal chats for example are not end-to-end-encrypted for usability reasons. Telegram and the founder deem trustworthy to me. But if they secretely collaborated with the Russian or U.S. government (or had to) at one point I would not be too surprised either.
For Whatsapp: I believe that Whatsapp is not and will not be secure. Here is a legitimate attack on Whatsapp not being safe by the Telegram founder Pavel Durov. Facebook is a commercial company earning money with ads. They will inject their business model in Whatsapp sooner or later and analyze the content of conversations.
I think it's safe to assume, that you should be very cautious on what you write on either platform.
Update from 2019/11/20: New backdoor in Whatsapp
|Completely free and independent||MEDIUM||Everyone who is afraid of Facebook collecting information about them, should love Telegram. Telegram is free forever. No ads. No subscription fees.|
|Usernames and public messages||MEDIUM||Send messages to me at http://t.me/mseibert.|
|Chatbots||MEDIUM||Chatbots allow all sorts of automations, integrations with other software, and games. Some examples of bots.|
|Stickers||MEDIUM||Stickers are like emoticons but much more entertaining and emotional in communication.|
|Possibility to chat with yourself||MEDIUM|
It is often very helpful to quickly send yourself a file, a picture or a text for later reference or use (e.g. on another device).
Update: It is possible with WhatsApp now technically. But creating such a chat and pinning it is probably something that most users don't do. They will likely not discover this feature.
|Options to edit and annotate pictures||POWERFUL||OKAY||MEDIUM||Whatsapp has cropping, annotation with text, big emoticons and freehand drawings. Telegram has all of that as well and much more. See below.|
|Improving pictures||MEDIUM||Telegram offers a lot of easy ways to edit pictures that you send: Enhance, Exposure, Contrast, Warmth, Saturation, Tint, Fade, Highlights, Shadows, Vignette, Grain, Blur, Sharpen, Curves|
|Who reads it and when||MEDIUM||Whatsapp allows you to see who read a message and when they read it. Telegram only allows you to see if the recipients have read the message but it does not show when they viewed it.|
|End-to-end encrypted chats||MEDIUM|
|Open source||MEDIUM||Telegram has an open API and a protocol free for everyone.|
|Mentions in groups||MEDIUM||You can address specific people in a chat with mentions.|
|Automatic Masks and Stickers||LOW|
Telegram can automatically add a hat or classes or a tie in a picture of people you take (masks). The result is often very funny and makes entertaining pictures.
|Unread syncing over devices||GOOD||OKAY||LOW||For Whatsapp, it is cumbersome to always authenticate Whatsapp web on your computer. That's why most people use it on their smartphone and thus do not need unread message syncing. Telegram does this seamlessly, and makes sure that you can rely on it only showing the stuff that is really important (and new).|
|Simple phone calling of people||LOW||I often use Telegram as my phone book both for calling and to look up numbers.|
|Notifications if your friends sign up||LOW||It's good for Telegram. Whatsapp does not need this feature as almost everyone seems to have it.|
|Message self-destruction||LOW||Most use cases that may benefit from this feature do not seem to happen often in my life.|
|Public channels and groups||LOW||Ability to make postings public to anyone on the web (for broadcasting).|
|Channels||LOW||Ability to let some people say something and others only read it.|
See all recipes here: https://ifttt.com/telegram
|Instant view for fast news consumption||LOW|
|Groups with up to 5,000 people||LOW||They are called super-groups.|
|Control whether people can see a room's history or not||MEDIUM|
|Optimal text formatting for conversations copied over from other software (e.g. JIRA)||LOW|