Let’s do a comparison of the three contenders.
WhatsApp is based in the USA, this free messaging app is available for Android and IOS devices. There is also a web version, although this does require the phone version to be connected on the WiFi which is a bit of a pain. Some businesses use WhatsApp to communicate with their customers. WhatsApp was started in 2009 and acquired by Facebook in 2014.
Telegram was launched in Russia in 2013 and is also a free messaging and calling app. It’s supported on a wide range of platforms including Android, IOS, Windows, MacOS and Linux.
Signal finally launched in 2015 after previous apps running under different names. The co-founder of WhatsApp got involved in 2018 with the launch of the non-profit Signal Foundation who have invested heavily in the app. Signal is available on Android, IOS and desktop versions are also available. Elon Musk of Tesla and SpaceX made a point of moving to Signal and recommending others follow.
Do they all offer encryption?
In short, yes they all offer robust end-to-end encryption but the implementation is different on each platform.
WhatsApp encrypts all traffic and data and is basically using the same protocols that Signal uses.
Telegram can encrypt all traffic but unlike WhatsApp and Signal, this is not on by default. Telegram uses uses MTProto encryption protocol which is based on 256-bit symmetric AES encryption, 2048-bit RSA encryption, and Diffie–Hellman key exchange.
Signal has its own TextSecure protocol which users AES-256, Curve25519 and HMAC-SHA256 combined with Double Ratchet Algorithm, prekeys and an extended triple Diffie-Hellman handshake. Other apps like WhatsApp, and Facebook Messenger use this protocol to offer end-to-end encryption. Signal’s app and end-to-end encryption is on by default.
What about your data?
WhatsApp uses store and forward, deleting the message as soon as it is delivered. If it can’t be delivered it is stored on their servers for 30 days whilst delivery is retried. The data is deleted after 30 days.
Telegram retains the data on their servers (heavily encrypted according to Telegram) for an undefined time.
Signal has no explicit data retention on its servers apart from technical information that is needed to operate the service. It also works on a store and forward basis until the message is delivered.
Will my data get collected for advertising purposes?
The full details on what data is collected and used is found on each apps privacy policies. In summary:
Whatsapp can share and collect data with Facebook for advertising purposes.
Telegram doesn’t use data for ad targeting but does plan to launch its own ad platform.
Signal doesn’t use ads at all.
Can they access my data?
WhatsApp will have access to detailed personal information (depending on your territory) which includes contacts, status, location, time logs, usage stats and other sensitive data.
Telegram collects user id’s and contact information including your number.
Signal collects and stores your number and also has access to your contacts to detect other Signal users (using hashed data).
So which app should I use?
To be honest, that’s a tough one that depends on how comfortable you are with sharing your data with a particular platform but there are a lot of users jumping ship from WhatsApp because of privacy concerns.