My opinion on Signal is it should definitely be preferred if one cares about security more than usability. I really cannot wait for it to have a "standalone" client (that is, that does not require the phone to be online as well).
There are other messaging apps, like Element (and the now defunct Keybase) which try to solve the same problems. So, I decided to keep that discussion for another future article (maybe).
Signal does not require the phone to be online as well. Source: just switched my phone off and still able to send and receive messages on the desktop app. WhatsApp, however, still very much requires the phone to be online for its web/desktop clients to work.
That said, Signal is still not a "standalone" app on desktop because it needs me to have installed and set up the app on my phone to link it to desktop. After this though, they are very much independent clients.
What happened to me is that I lost my phone, so I did not have an Android device to re-install Signal. I later managed to get back the SIM card and I assumed that I could use the Desktop client, but if I remember correctly it did not work. However, I will check again all of this