Horses for courses. Telegram is more user friendly, has excellent desktop apps, and scales brilliantly: it has some of the largest groups on the internet and has recently added audio calls to groups: this makes it much more interesting for me than, say, Zoom. There is some concern about ownership and location of servers: data does get stored on their servers. That said, it's extremely resilient, which is why it's being used in Belorussia to coordinate protests and Russia gave up trying to block it. There are also some concerns about encryption, especially with data being kept on the servers, but at least it doesn't leak telephone numbers like WhatsApp does.
Signal was designed for security which meant it is less user friendly than others but that minimal data was stored on their server. For example, until recently, you couldn't administer groups or have group calls because groups were essentially chains of bilateral chats. They have since done some very interesting research on zero knowledge group management which means that even you control the server you don't know who belongs to which group. In addition, they have have added support for group audio and video calls (up to 10), which is about all you can do without a server-based solution. The software has been peer-reviewed and the server has survived several subpoenas with Signal demonstrating how little information about users they can provide.
It's probably worth noting that there are other options such as Threema (costs € 4 one-off, developed and hosted in Switzerland and partly financed by a for suits version), which does not require a telephone number, and Wire, which has also had its software peer-reviewed.
Personally, I use Signal, Telegram and Threema for different groups. Interoperability would be great but prepared to use the right tool for the job and share as little compromising information as possible whatever the network, because even if you know the information can't be intercepted, you can't always be sure who's on the other end nor what they do with it.